diff --git a/src/include/rcube_imap_generic.php b/src/include/rcube_imap_generic.php
--- a/src/include/rcube_imap_generic.php
+++ b/src/include/rcube_imap_generic.php
@@ -1,6 +1,6 @@
 <?php
 
-/**
+/*
  +-----------------------------------------------------------------------+
  | This file is part of the Roundcube Webmail client                     |
  |                                                                       |
@@ -26,9 +26,6 @@
 
 /**
  * PHP based wrapper class to connect to an IMAP server
- *
- * @package    Framework
- * @subpackage Storage
  */
 class rcube_imap_generic
 {
@@ -37,44 +34,46 @@
     public $result;
     public $resultcode;
     public $selected;
-    public $data = array();
-    public $flags = array(
-        'SEEN'     => '\\Seen',
-        'DELETED'  => '\\Deleted',
-        'ANSWERED' => '\\Answered',
-        'DRAFT'    => '\\Draft',
-        'FLAGGED'  => '\\Flagged',
+    public $data  = [];
+    public $flags = [
+        'SEEN'      => '\\Seen',
+        'DELETED'   => '\\Deleted',
+        'ANSWERED'  => '\\Answered',
+        'DRAFT'     => '\\Draft',
+        'FLAGGED'   => '\\Flagged',
         'FORWARDED' => '$Forwarded',
-        'MDNSENT'  => '$MDNSent',
-        '*'        => '\\*',
-    );
+        'MDNSENT'   => '$MDNSent',
+        '*'         => '\\*',
+    ];
 
     protected $fp;
     protected $host;
+    protected $user;
     protected $cmd_tag;
     protected $cmd_num = 0;
     protected $resourceid;
-    protected $prefs             = array();
+    protected $extensions_enabled;
+    protected $prefs             = [];
     protected $logged            = false;
-    protected $capability        = array();
-    protected $capability_readed = false;
+    protected $capability        = [];
+    protected $capability_read   = false;
     protected $debug             = false;
     protected $debug_handler     = false;
 
-    const ERROR_OK       = 0;
-    const ERROR_NO       = -1;
-    const ERROR_BAD      = -2;
-    const ERROR_BYE      = -3;
-    const ERROR_UNKNOWN  = -4;
-    const ERROR_COMMAND  = -5;
-    const ERROR_READONLY = -6;
+    public const ERROR_OK       = 0;
+    public const ERROR_NO       = -1;
+    public const ERROR_BAD      = -2;
+    public const ERROR_BYE      = -3;
+    public const ERROR_UNKNOWN  = -4;
+    public const ERROR_COMMAND  = -5;
+    public const ERROR_READONLY = -6;
 
-    const COMMAND_NORESPONSE = 1;
-    const COMMAND_CAPABILITY = 2;
-    const COMMAND_LASTLINE   = 4;
-    const COMMAND_ANONYMIZED = 8;
+    public const COMMAND_NORESPONSE = 1;
+    public const COMMAND_CAPABILITY = 2;
+    public const COMMAND_LASTLINE   = 4;
+    public const COMMAND_ANONYMIZED = 8;
 
-    const DEBUG_LINE_LENGTH = 4098; // 4KB + 2B for \r\n
+    public const DEBUG_LINE_LENGTH = 4098; // 4KB + 2B for \r\n
 
 
     /**
@@ -84,7 +83,7 @@
      * @param bool   $endln      True if CRLF need to be added at the end of command
      * @param bool   $anonymized Don't write the given data to log but a placeholder
      *
-     * @param int Number of bytes sent, False on error
+     * @return int Number of bytes sent, False on error
      */
     protected function putLine($string, $endln = true, $anonymized = false)
     {
@@ -97,11 +96,9 @@
             $cut = $endln ? 2 : 0;
             if ($anonymized && preg_match('/^(A\d+ (?:[A-Z]+ )+)(.+)/', $string, $m)) {
                 $log = $m[1] . sprintf('****** [%d]', strlen($m[2]) - $cut);
-            }
-            else if ($anonymized) {
+            } elseif ($anonymized) {
                 $log = sprintf('****** [%d]', strlen($string) - $cut);
-            }
-            else {
+            } else {
                 $log = rtrim($string);
             }
 
@@ -123,7 +120,7 @@
 
     /**
      * Send command to the connection stream with Command Continuation
-     * Requests (RFC3501 7.5) and LITERAL+ (RFC2088) support
+     * Requests (RFC3501 7.5) and LITERAL+ (RFC2088) and LITERAL- (RFC7888) support.
      *
      * @param string $string     Command string
      * @param bool   $endln      True if CRLF need to be added at the end of command
@@ -131,7 +128,7 @@
      *
      * @return int|bool Number of bytes sent, False on error
      */
-    protected function putLineC($string, $endln=true, $anonymized=false)
+    protected function putLineC($string, $endln = true, $anonymized = false)
     {
         if (!$this->fp) {
             return false;
@@ -142,15 +139,20 @@
         }
 
         $res = 0;
-        if ($parts = preg_split('/(\{[0-9]+\}\r\n)/m', $string, -1, PREG_SPLIT_DELIM_CAPTURE)) {
-            for ($i=0, $cnt=count($parts); $i<$cnt; $i++) {
-                if ($i+1 < $cnt && preg_match('/^\{([0-9]+)\}\r\n$/', $parts[$i+1], $matches)) {
-                    // LITERAL+ support
-                    if ($this->prefs['literal+']) {
-                        $parts[$i+1] = sprintf("{%d+}\r\n", $matches[1]);
+        if ($parts = preg_split('/(\{[0-9]+\}\r\n)/m', $string, -1, \PREG_SPLIT_DELIM_CAPTURE)) {
+            for ($i = 0, $cnt = count($parts); $i < $cnt; $i++) {
+                if ($i + 1 < $cnt && preg_match('/^\{([0-9]+)\}\r\n$/', $parts[$i + 1], $matches)) {
+                    // LITERAL+/LITERAL- support
+                    $literal_plus = false;
+                    if (
+                        !empty($this->prefs['literal+'])
+                        || (!empty($this->prefs['literal-']) && $matches[1] <= 4096)
+                    ) {
+                        $parts[$i + 1] = sprintf("{%d+}\r\n", $matches[1]);
+                        $literal_plus = true;
                     }
 
-                    $bytes = $this->putLine($parts[$i].$parts[$i+1], false, $anonymized);
+                    $bytes = $this->putLine($parts[$i] . $parts[$i + 1], false, $anonymized);
                     if ($bytes === false) {
                         return false;
                     }
@@ -158,17 +160,16 @@
                     $res += $bytes;
 
                     // don't wait if server supports LITERAL+ capability
-                    if (!$this->prefs['literal+']) {
+                    if (!$literal_plus) {
                         $line = $this->readLine(1000);
                         // handle error in command
-                        if ($line[0] != '+') {
+                        if (!isset($line[0]) || $line[0] != '+') {
                             return false;
                         }
                     }
 
                     $i++;
-                }
-                else {
+                } else {
                     $bytes = $this->putLine($parts[$i], false, $anonymized);
                     if ($bytes === false) {
                         return false;
@@ -199,7 +200,7 @@
 
         do {
             if ($this->eof()) {
-                return $line ?: null;
+                return $line;
             }
 
             $buffer = fgets($this->fp, $size);
@@ -210,12 +211,43 @@
             }
 
             if ($this->debug) {
-                $this->debug('S: '. rtrim($buffer));
+                $this->debug('S: ' . rtrim($buffer));
             }
 
             $line .= $buffer;
+        } while (substr($buffer, -1) != "\n");
+
+        return $line;
+    }
+
+    /**
+     * Reads a line of data from the connection stream including all
+     * string continuation literals.
+     *
+     * @param int $size Buffer size
+     *
+     * @return string Line of text response
+     */
+    protected function readFullLine($size = 1024)
+    {
+        $line = $this->readLine($size);
+
+        // include all string literals untile the real end of "line"
+        while (preg_match('/\{([0-9]+)\}\r\n$/', $line, $m)) {
+            $bytes = $m[1];
+            $out   = '';
+
+            while (strlen($out) < $bytes) {
+                $out = $this->readBytes($bytes);
+                if ($out === '') {
+                    break;
+                }
+
+                $line .= $out;
+            }
+
+            $line .= $this->readLine($size);
         }
-        while (substr($buffer, -1) != "\n");
 
         return $line;
     }
@@ -224,8 +256,8 @@
      * Reads more data from the connection stream when provided
      * data contain string literal
      *
-     * @param string  $line    Response text
-     * @param bool    $escape  Enables escaping
+     * @param string $line   Response text
+     * @param bool   $escape Enables escaping
      *
      * @return string Line of text response
      */
@@ -239,7 +271,7 @@
 
             while (strlen($out) < $bytes) {
                 $line = $this->readBytes($bytes);
-                if ($line === null) {
+                if ($line === '') {
                     break;
                 }
 
@@ -265,9 +297,9 @@
         $len  = 0;
 
         while ($len < $bytes && !$this->eof()) {
-            $d = fread($this->fp, $bytes-$len);
+            $d = fread($this->fp, $bytes - $len);
             if ($this->debug) {
-                $this->debug('S: '. $d);
+                $this->debug('S: ' . $d);
             }
             $data .= $d;
             $data_len = strlen($data);
@@ -289,14 +321,15 @@
      */
     protected function readReply(&$untagged = null)
     {
-        do {
+        while (true) {
             $line = trim($this->readLine(1024));
             // store untagged response lines
-            if ($line[0] == '*') {
+            if (isset($line[0]) && $line[0] == '*') {
                 $untagged[] = $line;
+            } else {
+                break;
             }
         }
-        while ($line[0] == '*');
 
         if ($untagged) {
             $untagged = implode("\n", $untagged);
@@ -321,14 +354,11 @@
 
             if ($res == 'OK') {
                 $this->errornum = self::ERROR_OK;
-            }
-            else if ($res == 'NO') {
+            } elseif ($res == 'NO') {
                 $this->errornum = self::ERROR_NO;
-            }
-            else if ($res == 'BAD') {
+            } elseif ($res == 'BAD') {
                 $this->errornum = self::ERROR_BAD;
-            }
-            else if ($res == 'BYE') {
+            } elseif ($res == 'BYE') {
                 $this->closeSocket();
                 $this->errornum = self::ERROR_BYE;
             }
@@ -336,26 +366,25 @@
             if ($str) {
                 $str = trim($str);
                 // get response string and code (RFC5530)
-                if (preg_match("/^\[([a-z-]+)\]/i", $str, $m)) {
+                if (preg_match('/^\\[([a-z-]+)\\]/i', $str, $m)) {
                     $this->resultcode = strtoupper($m[1]);
                     $str = trim(substr($str, strlen($m[1]) + 2));
-                }
-                else {
+                } else {
                     $this->resultcode = null;
                     // parse response for [APPENDUID 1204196876 3456]
-                    if (preg_match("/^\[APPENDUID [0-9]+ ([0-9]+)\]/i", $str, $m)) {
+                    if (preg_match('/^\\[APPENDUID [0-9]+ ([0-9]+)\\]/i', $str, $m)) {
                         $this->data['APPENDUID'] = $m[1];
                     }
                     // parse response for [COPYUID 1204196876 3456:3457 123:124]
-                    else if (preg_match("/^\[COPYUID [0-9]+ ([0-9,:]+) ([0-9,:]+)\]/i", $str, $m)) {
-                        $this->data['COPYUID'] = array($m[1], $m[2]);
+                    elseif (preg_match('/^\\[COPYUID [0-9]+ ([0-9,:]+) ([0-9,:]+)\\]/i', $str, $m)) {
+                        $this->data['COPYUID'] = [$m[1], $m[2]];
                     }
                 }
 
                 $this->result = $str;
 
                 if ($this->errornum != self::ERROR_OK) {
-                    $this->error = $err_prefix ? $err_prefix.$str : $str;
+                    $this->error = $err_prefix ? $err_prefix . $str : $str;
                 }
             }
 
@@ -372,7 +401,7 @@
      */
     protected function eof()
     {
-        if (!is_resource($this->fp)) {
+        if (!$this->fp) {
             return true;
         }
 
@@ -380,8 +409,8 @@
         // by the server, feof() will hang.
         $start = microtime(true);
 
-        if (feof($this->fp) ||
-            ($this->prefs['timeout'] && (microtime(true) - $start > $this->prefs['timeout']))
+        if (feof($this->fp)
+            || ($this->prefs['timeout'] && (microtime(true) - $start > $this->prefs['timeout']))
         ) {
             $this->closeSocket();
             return true;
@@ -395,8 +424,10 @@
      */
     protected function closeSocket()
     {
-        @fclose($this->fp);
-        $this->fp = null;
+        if ($this->fp) {
+            fclose($this->fp);
+            $this->fp = null;
+        }
     }
 
     /**
@@ -450,18 +481,17 @@
      */
     protected function hasCapability($name)
     {
-        if (empty($this->capability) || $name == '') {
+        if (empty($this->capability) || empty($name)) {
             return false;
         }
 
         if (in_array($name, $this->capability)) {
             return true;
-        }
-        else if (strpos($name, '=')) {
+        } elseif (strpos($name, '=')) {
             return false;
         }
 
-        $result = array();
+        $result = [];
         foreach ($this->capability as $cap) {
             $entry = explode('=', $cap);
             if ($entry[0] == $name) {
@@ -485,8 +515,7 @@
 
         if (!empty($result)) {
             return $result;
-        }
-        else if ($this->capability_readed) {
+        } elseif ($this->capability_read) {
             return false;
         }
 
@@ -498,7 +527,7 @@
             $this->parseCapability($result[1]);
         }
 
-        $this->capability_readed = true;
+        $this->capability_read = true;
 
         return $this->hasCapability($name);
     }
@@ -508,8 +537,8 @@
      */
     public function clearCapability()
     {
-        $this->capability        = array();
-        $this->capability_readed = false;
+        $this->capability        = [];
+        $this->capability_read = false;
     }
 
     /**
@@ -519,14 +548,14 @@
      * @param string $pass Password
      * @param string $type Authentication type (PLAIN/CRAM-MD5/DIGEST-MD5)
      *
-     * @return resource Connection resourse on success, error code on error
+     * @return resource|int Connection resource on success, error code on error
      */
     protected function authenticate($user, $pass, $type = 'PLAIN')
     {
         if ($type == 'CRAM-MD5' || $type == 'DIGEST-MD5') {
             if ($type == 'DIGEST-MD5' && !class_exists('Auth_SASL')) {
                 return $this->setError(self::ERROR_BYE,
-                    "The Auth_SASL package is required for DIGEST-MD5 authentication");
+                    'The Auth_SASL package is required for DIGEST-MD5 authentication');
             }
 
             $this->putLine($this->nextTag() . " AUTHENTICATE $type");
@@ -534,8 +563,7 @@
 
             if ($line[0] == '+') {
                 $challenge = substr($line, 2);
-            }
-            else {
+            } else {
                 return $this->parseResult($line);
             }
 
@@ -543,17 +571,17 @@
                 // RFC2195: CRAM-MD5
                 $ipad = '';
                 $opad = '';
-                $xor  = function($str1, $str2) {
+                $xor  = static function ($str1, $str2) {
                     $result = '';
                     $size   = strlen($str1);
-                    for ($i=0; $i<$size; $i++) {
+                    for ($i = 0; $i < $size; $i++) {
                         $result .= chr(ord($str1[$i]) ^ ord($str2[$i]));
                     }
                     return $result;
                 };
 
                 // initialize ipad, opad
-                for ($i=0; $i<64; $i++) {
+                for ($i = 0; $i < 64; $i++) {
                     $ipad .= chr(0x36);
                     $opad .= chr(0x5C);
                 }
@@ -562,26 +590,24 @@
                 $pass = str_pad($pass, 64, chr(0));
 
                 // generate hash
-                $hash  = md5($xor($pass, $opad) . pack("H*",
+                $hash  = md5($xor($pass, $opad) . pack('H*',
                     md5($xor($pass, $ipad) . base64_decode($challenge))));
                 $reply = base64_encode($user . ' ' . $hash);
 
                 // send result
                 $this->putLine($reply, true, true);
-            }
-            else {
+            } else {
                 // RFC2831: DIGEST-MD5
                 // proxy authorization
                 if (!empty($this->prefs['auth_cid'])) {
                     $authc = $this->prefs['auth_cid'];
                     $pass  = $this->prefs['auth_pw'];
-                }
-                else {
+                } else {
                     $authc = $user;
                     $user  = '';
                 }
 
-                $auth_sasl = new Auth_SASL;
+                $auth_sasl = new Auth_SASL();
                 $auth_sasl = $auth_sasl->factory('digestmd5');
                 $reply     = base64_encode($auth_sasl->getResponse($authc, $pass,
                     base64_decode($challenge), $this->host, 'imap', $user));
@@ -599,7 +625,7 @@
                 $challenge = base64_decode($challenge);
                 if (strpos($challenge, 'rspauth=') === false) {
                     return $this->setError(self::ERROR_BAD,
-                        "Unexpected response from server to DIGEST-MD5 response");
+                        'Unexpected response from server to DIGEST-MD5 response');
                 }
 
                 $this->putLine('');
@@ -607,21 +633,20 @@
 
             $line   = $this->readReply();
             $result = $this->parseResult($line);
-        }
-        else if ($type == 'GSSAPI') {
+        } elseif ($type == 'GSSAPI') {
             if (!extension_loaded('krb5')) {
                 return $this->setError(self::ERROR_BYE,
-                    "The krb5 extension is required for GSSAPI authentication");
+                    'The krb5 extension is required for GSSAPI authentication');
             }
 
             if (empty($this->prefs['gssapi_cn'])) {
                 return $this->setError(self::ERROR_BYE,
-                    "The gssapi_cn parameter is required for GSSAPI authentication");
+                    'The gssapi_cn parameter is required for GSSAPI authentication');
             }
 
             if (empty($this->prefs['gssapi_context'])) {
                 return $this->setError(self::ERROR_BYE,
-                    "The gssapi_context parameter is required for GSSAPI authentication");
+                    'The gssapi_context parameter is required for GSSAPI authentication');
             }
 
             putenv('KRB5CCNAME=' . $this->prefs['gssapi_cn']);
@@ -635,13 +660,12 @@
                 $token   = '';
                 $success = $gssapicontext->initSecContext($this->prefs['gssapi_context'], null, null, null, $token);
                 $token   = base64_encode($token);
-            }
-            catch (Exception $e) {
-                trigger_error($e->getMessage(), E_USER_WARNING);
-                return $this->setError(self::ERROR_BYE, "GSSAPI authentication failed");
+            } catch (Exception $e) {
+                trigger_error($e->getMessage(), \E_USER_WARNING);
+                return $this->setError(self::ERROR_BYE, 'GSSAPI authentication failed');
             }
 
-            $this->putLine($this->nextTag() . " AUTHENTICATE GSSAPI " . $token);
+            $this->putLine($this->nextTag() . ' AUTHENTICATE GSSAPI ' . $token);
             $line = trim($this->readReply());
 
             if ($line[0] != '+') {
@@ -652,11 +676,11 @@
                 $itoken = base64_decode(substr($line, 2));
 
                 if (!$gssapicontext->unwrap($itoken, $itoken)) {
-                    throw new Exception("GSSAPI SASL input token unwrap failed");
+                    throw new Exception('GSSAPI SASL input token unwrap failed');
                 }
 
                 if (strlen($itoken) < 4) {
-                    throw new Exception("GSSAPI SASL input token invalid");
+                    throw new Exception('GSSAPI SASL input token invalid');
                 }
 
                 // Integrity/encryption layers are not supported. The first bit
@@ -664,33 +688,30 @@
                 // 0x00 should not occur, but support broken implementations.
                 $server_layers = ord($itoken[0]);
                 if ($server_layers && ($server_layers & 0x1) != 0x1) {
-                    throw new Exception("Server requires GSSAPI SASL integrity/encryption");
+                    throw new Exception('Server requires GSSAPI SASL integrity/encryption');
                 }
 
                 // Construct output token. 0x01 in the first octet = SASL layer "none",
                 // zero in the following three octets = no data follows.
                 // See https://github.com/cyrusimap/cyrus-sasl/blob/e41cfb986c1b1935770de554872247453fdbb079/plugins/gssapi.c#L1284
-                if (!$gssapicontext->wrap(pack("CCCC", 0x1, 0, 0, 0), $otoken, true)) {
-                    throw new Exception("GSSAPI SASL output token wrap failed");
+                if (!$gssapicontext->wrap(pack('CCCC', 0x1, 0, 0, 0), $otoken, true)) {
+                    throw new Exception('GSSAPI SASL output token wrap failed');
                 }
-            }
-            catch (Exception $e) {
-                trigger_error($e->getMessage(), E_USER_WARNING);
-                return $this->setError(self::ERROR_BYE, "GSSAPI authentication failed");
+            } catch (Exception $e) {
+                trigger_error($e->getMessage(), \E_USER_WARNING);
+                return $this->setError(self::ERROR_BYE, 'GSSAPI authentication failed');
             }
 
             $this->putLine(base64_encode($otoken));
 
             $line   = $this->readReply();
             $result = $this->parseResult($line);
-        }
-        else if ($type == 'PLAIN') {
+        } elseif ($type == 'PLAIN') {
             // proxy authorization
             if (!empty($this->prefs['auth_cid'])) {
                 $authc = $this->prefs['auth_cid'];
                 $pass  = $this->prefs['auth_pw'];
-            }
-            else {
+            } else {
                 $authc = $user;
                 $user  = '';
             }
@@ -699,11 +720,10 @@
 
             // RFC 4959 (SASL-IR): save one round trip
             if ($this->getCapability('SASL-IR')) {
-                list($result, $line) = $this->execute("AUTHENTICATE PLAIN", array($reply),
+                [$result, $line] = $this->execute('AUTHENTICATE PLAIN', [$reply],
                     self::COMMAND_LASTLINE | self::COMMAND_CAPABILITY | self::COMMAND_ANONYMIZED);
-            }
-            else {
-                $this->putLine($this->nextTag() . " AUTHENTICATE PLAIN");
+            } else {
+                $this->putLine($this->nextTag() . ' AUTHENTICATE PLAIN');
                 $line = trim($this->readReply());
 
                 if ($line[0] != '+') {
@@ -715,9 +735,8 @@
                 $line   = $this->readReply();
                 $result = $this->parseResult($line);
             }
-        }
-        else if ($type == 'LOGIN') {
-            $this->putLine($this->nextTag() . " AUTHENTICATE LOGIN");
+        } elseif ($type == 'LOGIN') {
+            $this->putLine($this->nextTag() . ' AUTHENTICATE LOGIN');
 
             $line = trim($this->readReply());
             if ($line[0] != '+') {
@@ -736,6 +755,24 @@
 
             $line   = $this->readReply();
             $result = $this->parseResult($line);
+        } elseif (($type == 'XOAUTH2') || ($type == 'OAUTHBEARER')) {
+            $auth = ($type == 'XOAUTH2')
+                ? base64_encode("user=$user\1auth=$pass\1\1")  // XOAUTH: original extension, still widely used
+                : base64_encode("n,a=$user,\1auth=$pass\1\1"); // OAUTHBEARER: official RFC 7628
+            $this->putLine($this->nextTag() . " AUTHENTICATE $type $auth", true, true);
+
+            $line = trim($this->readReply());
+
+            if ($line[0] == '+') {
+                // send empty line
+                $this->putLine('', true, true);
+                $line = $this->readReply();
+            }
+
+            $result = $this->parseResult($line);
+        } else {
+            $line  = 'not supported';
+            $result = self::ERROR_UNKNOWN;
         }
 
         if ($result === self::ERROR_OK) {
@@ -753,20 +790,20 @@
     /**
      * LOGIN Authentication
      *
-     * @param string $user Username
-     * @param string $pass Password
+     * @param string $user     Username
+     * @param string $password Password
      *
-     * @return resource Connection resourse on success, error code on error
+     * @return resource|int Connection resource on success, error code on error
      */
     protected function login($user, $password)
     {
         // Prevent from sending credentials in plain text when connection is not secure
         if ($this->getCapability('LOGINDISABLED')) {
-            return $this->setError(self::ERROR_BAD, "Login disabled by IMAP server");
+            return $this->setError(self::ERROR_BAD, 'Login disabled by IMAP server');
         }
 
-        list($code, $response) = $this->execute('LOGIN', array(
-            $this->escape($user), $this->escape($password)), self::COMMAND_CAPABILITY | self::COMMAND_ANONYMIZED);
+        [$code, $response] = $this->execute('LOGIN', [$this->escape($user, true), $this->escape($password, true)],
+            self::COMMAND_CAPABILITY | self::COMMAND_ANONYMIZED);
 
         // re-set capabilities list if untagged CAPABILITY response provided
         if (preg_match('/\* CAPABILITY (.+)/i', $response, $matches)) {
@@ -787,20 +824,19 @@
      */
     public function getHierarchyDelimiter()
     {
-        if (isset($this->prefs['delimiter'])) {
+        if (!empty($this->prefs['delimiter'])) {
             return $this->prefs['delimiter'];
         }
 
         // try (LIST "" ""), should return delimiter (RFC2060 Sec 6.3.8)
-        list($code, $response) = $this->execute('LIST',
-            array($this->escape(''), $this->escape('')));
+        [$code, $response] = $this->execute('LIST', [$this->escape(''), $this->escape('')]);
 
         if ($code == self::ERROR_OK) {
             $args = $this->tokenizeResponse($response, 4);
             $delimiter = $args[3];
 
             if (strlen($delimiter) > 0) {
-                return ($this->prefs['delimiter'] = $delimiter);
+                return $this->prefs['delimiter'] = $delimiter;
             }
         }
     }
@@ -820,22 +856,22 @@
             return self::ERROR_BAD;
         }
 
-        list($code, $response) = $this->execute('NAMESPACE');
+        [$code, $response] = $this->execute('NAMESPACE');
 
         if ($code == self::ERROR_OK && preg_match('/^\* NAMESPACE /', $response)) {
             $response = substr($response, 11);
             $data     = $this->tokenizeResponse($response);
         }
 
-        if (!is_array($data)) {
+        if (!isset($data) || !is_array($data)) {
             return $code;
         }
 
-        $this->prefs['namespace'] = array(
+        $this->prefs['namespace'] = [
             'personal' => $data[0],
             'other'    => $data[1],
             'shared'   => $data[2],
-        );
+        ];
 
         return $this->prefs['namespace'];
     }
@@ -850,7 +886,7 @@
      *
      * @return bool True on success, False on failure
      */
-    public function connect($host, $user, $password, $options = array())
+    public function connect($host, $user, $password, $options = [])
     {
         // configure
         $this->set_prefs($options);
@@ -862,17 +898,17 @@
 
         // check input
         if (empty($host)) {
-            $this->setError(self::ERROR_BAD, "Empty host");
+            $this->setError(self::ERROR_BAD, 'Empty host');
             return false;
         }
 
         if (empty($user)) {
-            $this->setError(self::ERROR_NO, "Empty user");
+            $this->setError(self::ERROR_NO, 'Empty user');
             return false;
         }
 
         if (empty($password) && empty($options['gssapi_cn'])) {
-            $this->setError(self::ERROR_NO, "Empty password");
+            $this->setError(self::ERROR_NO, 'Empty password');
             return false;
         }
 
@@ -881,13 +917,13 @@
             return false;
         }
 
-        // Send ID info
-        if (!empty($this->prefs['ident']) && $this->getCapability('ID')) {
-            $this->data['ID'] = $this->id($this->prefs['ident']);
+        // Send pre authentication ID info (#7860)
+        if (!empty($this->prefs['preauth_ident']) && $this->getCapability('ID')) {
+            $this->data['ID'] = $this->id($this->prefs['preauth_ident']);
         }
 
         $auth_method  = $this->prefs['auth_type'];
-        $auth_methods = array();
+        $auth_methods = [];
         $result       = null;
 
         // check for supported auth methods
@@ -897,7 +933,7 @@
             }
 
             // Use best (for security) supported authentication method
-            $all_methods = array('DIGEST-MD5', 'CRAM-MD5', 'CRAM_MD5', 'PLAIN', 'LOGIN');
+            $all_methods = ['DIGEST-MD5', 'CRAM-MD5', 'CRAM_MD5', 'PLAIN', 'LOGIN'];
 
             if (!empty($this->prefs['gssapi_cn'])) {
                 array_unshift($all_methods, 'GSSAPI');
@@ -916,7 +952,7 @@
         }
 
         // pre-login capabilities can be not complete
-        $this->capability_readed = false;
+        $this->capability_read = false;
 
         // Authenticate
         switch ($auth_method) {
@@ -927,6 +963,8 @@
             case 'GSSAPI':
             case 'PLAIN':
             case 'LOGIN':
+            case 'XOAUTH2':
+            case 'OAUTHBEARER':
                 $result = $this->authenticate($user, $password, $auth_method);
                 break;
 
@@ -943,8 +981,14 @@
             if (!empty($this->prefs['force_caps'])) {
                 $this->clearCapability();
             }
+
             $this->logged = true;
 
+            // Send ID info after authentication to ensure reliable result (#7517)
+            if (!empty($this->prefs['ident']) && $this->getCapability('ID')) {
+                $this->data['ID'] = $this->id($this->prefs['ident']);
+            }
+
             return true;
         }
 
@@ -966,13 +1010,12 @@
         $this->error    = '';
         $this->errornum = self::ERROR_OK;
 
-        if (!$this->prefs['port']) {
-            $this->prefs['port'] = 143;
-        }
+        $port     = empty($this->prefs['port']) ? 143 : $this->prefs['port'];
+        $ssl_mode = $this->prefs['ssl_mode'] ?? null;
 
         // check for SSL
-        if (!empty($this->prefs['ssl_mode']) && $this->prefs['ssl_mode'] != 'tls') {
-            $host = $this->prefs['ssl_mode'] . '://' . $host;
+        if (!empty($ssl_mode) && $ssl_mode != 'tls') {
+            $host = $ssl_mode . '://' . $host;
         }
 
         if (empty($this->prefs['timeout']) || $this->prefs['timeout'] < 0) {
@@ -983,22 +1026,22 @@
             // set connection identifier for debug output
             $this->resourceid = strtoupper(substr(md5(microtime() . $host . $this->user), 0, 4));
 
-            $_host = ($this->prefs['ssl_mode'] == 'tls' ? 'tls://' : '') . $host . ':' . $this->prefs['port'];
+            $_host = ($ssl_mode == 'tls' ? 'tls://' : '') . $host . ':' . $port;
             $this->debug("Connecting to $_host...");
         }
 
         if (!empty($this->prefs['socket_options'])) {
-            $context  = stream_context_create($this->prefs['socket_options']);
-            $this->fp = stream_socket_client($host . ':' . $this->prefs['port'], $errno, $errstr,
-                $this->prefs['timeout'], STREAM_CLIENT_CONNECT, $context);
-        }
-        else {
-            $this->fp = @fsockopen($host, $this->prefs['port'], $errno, $errstr, $this->prefs['timeout']);
+            $options  = array_intersect_key($this->prefs['socket_options'], ['ssl' => 1]);
+            $context  = stream_context_create($options);
+            $this->fp = stream_socket_client($host . ':' . $port, $errno, $errstr,
+                $this->prefs['timeout'], \STREAM_CLIENT_CONNECT, $context);
+        } else {
+            $this->fp = @fsockopen($host, $port, $errno, $errstr, $this->prefs['timeout']);
         }
 
         if (!$this->fp) {
-            $this->setError(self::ERROR_BAD, sprintf("Could not connect to %s:%d: %s",
-                $host, $this->prefs['port'], $errstr ?: "Unknown reason"));
+            $this->setError(self::ERROR_BAD, sprintf('Could not connect to %s:%d: %s',
+                $host, $port, $errstr ?: 'Unknown reason'));
 
             return false;
         }
@@ -1010,15 +1053,16 @@
         $line = trim(fgets($this->fp, 8192));
 
         if ($this->debug && $line) {
-            $this->debug('S: '. $line);
+            $this->debug('S: ' . $line);
         }
 
         // Connected to wrong port or connection error?
         if (!preg_match('/^\* (OK|PREAUTH)/i', $line)) {
-            if ($line)
-                $error = sprintf("Wrong startup greeting (%s:%d): %s", $host, $this->prefs['port'], $line);
-            else
-                $error = sprintf("Empty startup greeting (%s:%d)", $host, $this->prefs['port']);
+            if ($line) {
+                $error = sprintf('Wrong startup greeting (%s:%d): %s', $host, $port, $line);
+            } else {
+                $error = sprintf('Empty startup greeting (%s:%d)', $host, $port);
+            }
 
             $this->setError(self::ERROR_BAD, $error);
             $this->closeConnection();
@@ -1033,27 +1077,26 @@
         }
 
         // TLS connection
-        if ($this->prefs['ssl_mode'] == 'tls' && $this->getCapability('STARTTLS')) {
+        if ($ssl_mode == 'tls' && $this->getCapability('STARTTLS')) {
             $res = $this->execute('STARTTLS');
 
-            if ($res[0] != self::ERROR_OK) {
+            if (empty($res) || $res[0] != self::ERROR_OK) {
                 $this->closeConnection();
                 return false;
             }
 
             if (isset($this->prefs['socket_options']['ssl']['crypto_method'])) {
                 $crypto_method = $this->prefs['socket_options']['ssl']['crypto_method'];
-            }
-            else {
+            } else {
                 // There is no flag to enable all TLS methods. Net_SMTP
                 // handles enabling TLS similarly.
-                $crypto_method = STREAM_CRYPTO_METHOD_TLS_CLIENT
-                    | @STREAM_CRYPTO_METHOD_TLSv1_1_CLIENT
-                    | @STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT;
+                $crypto_method = \STREAM_CRYPTO_METHOD_TLS_CLIENT
+                    | @\STREAM_CRYPTO_METHOD_TLSv1_1_CLIENT
+                    | @\STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT;
             }
 
             if (!stream_socket_enable_crypto($this->fp, true, $crypto_method)) {
-                $this->setError(self::ERROR_BAD, "Unable to negotiate TLS");
+                $this->setError(self::ERROR_BAD, 'Unable to negotiate TLS');
                 $this->closeConnection();
                 return false;
             }
@@ -1078,14 +1121,13 @@
         // set auth method
         if (!empty($this->prefs['auth_type'])) {
             $this->prefs['auth_type'] = strtoupper($this->prefs['auth_type']);
-        }
-        else {
+        } else {
             $this->prefs['auth_type'] = 'CHECK';
         }
 
         // disabled capabilities
         if (!empty($this->prefs['disabled_caps'])) {
-            $this->prefs['disabled_caps'] = array_map('strtoupper', (array)$this->prefs['disabled_caps']);
+            $this->prefs['disabled_caps'] = array_map('strtoupper', (array) $this->prefs['disabled_caps']);
         }
 
         // additional message flags
@@ -1115,6 +1157,7 @@
         }
 
         $this->closeSocket();
+        $this->clearCapability();
     }
 
     /**
@@ -1123,7 +1166,7 @@
      * @param string $mailbox      Mailbox name
      * @param array  $qresync_data QRESYNC data (RFC5162)
      *
-     * @return boolean True on success, false on error
+     * @return bool True on success, false on error
      */
     public function select($mailbox, $qresync_data = null)
     {
@@ -1135,7 +1178,7 @@
             return true;
         }
 
-        $params = array($this->escape($mailbox));
+        $params = [$this->escape($mailbox)];
 
         // QRESYNC data items
         //    0. the last known UIDVALIDITY,
@@ -1148,10 +1191,10 @@
                 $qresync_data[2] = self::compressMessageSet($qresync_data[2]);
             }
 
-            $params[] = array('QRESYNC', $qresync_data);
+            $params[] = ['QRESYNC', $qresync_data];
         }
 
-        list($code, $response) = $this->execute('SELECT', $params);
+        [$code, $response] = $this->execute('SELECT', $params);
 
         if ($code == self::ERROR_OK) {
             $this->clear_mailbox_cache();
@@ -1164,58 +1207,57 @@
                     $pos   += 7;
 
                     switch ($token) {
-                    case 'UIDNEXT':
-                    case 'UIDVALIDITY':
-                    case 'UNSEEN':
-                        if ($len = strspn($line, '0123456789', $pos)) {
-                            $this->data[$token] = (int) substr($line, $pos, $len);
-                        }
-                        break;
+                        case 'UIDNEXT':
+                        case 'UIDVALIDITY':
+                        case 'UNSEEN':
+                            if ($len = strspn($line, '0123456789', $pos)) {
+                                $this->data[$token] = (int) substr($line, $pos, $len);
+                            }
+                            break;
 
-                    case 'HIGHESTMODSEQ':
-                        if ($len = strspn($line, '0123456789', $pos)) {
-                            $this->data[$token] = (string) substr($line, $pos, $len);
-                        }
-                        break;
+                        case 'HIGHESTMODSEQ':
+                            if ($len = strspn($line, '0123456789', $pos)) {
+                                $this->data[$token] = (string) substr($line, $pos, $len);
+                            }
+                            break;
 
-                    case 'NOMODSEQ':
-                        $this->data[$token] = true;
-                        break;
+                        case 'NOMODSEQ':
+                            $this->data[$token] = true;
+                            break;
 
-                    case 'PERMANENTFLAGS':
-                        $start = strpos($line, '(', $pos);
-                        $end   = strrpos($line, ')');
-                        if ($start && $end) {
-                            $flags = substr($line, $start + 1, $end - $start - 1);
-                            $this->data[$token] = explode(' ', $flags);
-                        }
-                        break;
+                        case 'PERMANENTFLAGS':
+                            $start = strpos($line, '(', $pos);
+                            $end   = strrpos($line, ')');
+                            if ($start && $end) {
+                                $flags = substr($line, $start + 1, $end - $start - 1);
+                                $this->data[$token] = explode(' ', $flags);
+                            }
+                            break;
                     }
-                }
-                else if (preg_match('/^\* ([0-9]+) (EXISTS|RECENT|FETCH)/i', $line, $match)) {
+                } elseif (preg_match('/^\* ([0-9]+) (EXISTS|RECENT|FETCH)/i', $line, $match)) {
                     $token = strtoupper($match[2]);
                     switch ($token) {
-                    case 'EXISTS':
-                    case 'RECENT':
-                        $this->data[$token] = (int) $match[1];
-                        break;
+                        case 'EXISTS':
+                        case 'RECENT':
+                            $this->data[$token] = (int) $match[1];
+                            break;
 
-                    case 'FETCH':
-                        // QRESYNC FETCH response (RFC5162)
-                        $line       = substr($line, strlen($match[0]));
-                        $fetch_data = $this->tokenizeResponse($line, 1);
-                        $data       = array('id' => $match[1]);
+                        case 'FETCH':
+                            // QRESYNC FETCH response (RFC5162)
+                            $line       = substr($line, strlen($match[0]));
+                            $fetch_data = $this->tokenizeResponse($line, 1);
+                            $data       = ['id' => $match[1]];
 
-                        for ($i=0, $size=count($fetch_data); $i<$size; $i+=2) {
-                            $data[strtolower($fetch_data[$i])] = $fetch_data[$i+1];
-                        }
+                            for ($i = 0, $size = count($fetch_data); $i < $size; $i += 2) {
+                                $data[strtolower($fetch_data[$i])] = $fetch_data[$i + 1];
+                            }
 
-                        $this->data['QRESYNC'][$data['uid']] = $data;
-                        break;
+                            $this->data['QRESYNC'][$data['uid']] = $data;
+                            break;
                     }
                 }
                 // QRESYNC VANISHED response (RFC5162)
-                else if (preg_match('/^\* VANISHED [()EARLIER]*/i', $line, $match)) {
+                elseif (preg_match('/^\* VANISHED [()EARLIER]*/i', $line, $match)) {
                     $line   = substr($line, strlen($match[0]));
                     $v_data = $this->tokenizeResponse($line, 1);
 
@@ -1241,9 +1283,10 @@
      *                        in RFC3501: UIDNEXT, UIDVALIDITY, RECENT
      *
      * @return array Status item-value hash
+     *
      * @since 0.5-beta
      */
-    public function status($mailbox, $items = array())
+    public function status($mailbox, $items = [])
     {
         if (!strlen($mailbox)) {
             return false;
@@ -1256,14 +1299,14 @@
             $items[] = 'UNSEEN';
         }
 
-        list($code, $response) = $this->execute('STATUS',
-            array($this->escape($mailbox), '(' . implode(' ', $items) . ')'), 0, '/^\* STATUS /i');
+        [$code, $response] = $this->execute('STATUS',
+            [$this->escape($mailbox), '(' . implode(' ', $items) . ')'], 0, '/^\* STATUS /i');
 
         if ($code == self::ERROR_OK && $response) {
-            $result   = array();
+            $result   = [];
             $response = substr($response, 9); // remove prefix "* STATUS "
 
-            list($mbox, $items) = $this->tokenizeResponse($response, 2);
+            [$mbox, $items] = $this->tokenizeResponse($response, 2);
 
             // Fix for #1487859. Some buggy server returns not quoted
             // folder name with spaces. Let's try to handle this situation
@@ -1276,11 +1319,11 @@
                 return $result;
             }
 
-            for ($i=0, $len=count($items); $i<$len; $i += 2) {
-                $result[$items[$i]] = $items[$i+1];
+            for ($i = 0, $len = count($items); $i < $len; $i += 2) {
+                $result[$items[$i]] = $items[$i + 1];
             }
 
-            $this->data['STATUS:'.$mailbox] = $result;
+            $this->data['STATUS:' . $mailbox] = $result;
 
             return $result;
         }
@@ -1294,7 +1337,7 @@
      * @param string       $mailbox  Mailbox name
      * @param string|array $messages Message UIDs to expunge
      *
-     * @return boolean True on success, False on error
+     * @return bool True on success, False on error
      */
     public function expunge($mailbox, $messages = null)
     {
@@ -1302,8 +1345,8 @@
             return false;
         }
 
-        if (!$this->data['READ-WRITE']) {
-            $this->setError(self::ERROR_READONLY, "Mailbox is read-only");
+        if (empty($this->data['READ-WRITE'])) {
+            $this->setError(self::ERROR_READONLY, 'Mailbox is read-only');
             return false;
         }
 
@@ -1312,9 +1355,8 @@
 
         if (!empty($messages) && $messages != '*' && $this->hasCapability('UIDPLUS')) {
             $messages = self::compressMessageSet($messages);
-            $result   = $this->execute('UID EXPUNGE', array($messages), self::COMMAND_NORESPONSE);
-        }
-        else {
+            $result   = $this->execute('UID EXPUNGE', [$messages], self::COMMAND_NORESPONSE);
+        } else {
             $result = $this->execute('EXPUNGE', null, self::COMMAND_NORESPONSE);
         }
 
@@ -1329,7 +1371,8 @@
     /**
      * Executes CLOSE command
      *
-     * @return boolean True on success, False on error
+     * @return bool True on success, False on error
+     *
      * @since 0.5
      */
     public function close()
@@ -1349,12 +1392,11 @@
      *
      * @param string $mailbox Mailbox name
      *
-     * @return boolean True on success, False on error
+     * @return bool True on success, False on error
      */
     public function subscribe($mailbox)
     {
-        $result = $this->execute('SUBSCRIBE', array($this->escape($mailbox)),
-            self::COMMAND_NORESPONSE);
+        $result = $this->execute('SUBSCRIBE', [$this->escape($mailbox)], self::COMMAND_NORESPONSE);
 
         return $result == self::ERROR_OK;
     }
@@ -1364,12 +1406,11 @@
      *
      * @param string $mailbox Mailbox name
      *
-     * @return boolean True on success, False on error
+     * @return bool True on success, False on error
      */
     public function unsubscribe($mailbox)
     {
-        $result = $this->execute('UNSUBSCRIBE', array($this->escape($mailbox)),
-            self::COMMAND_NORESPONSE);
+        $result = $this->execute('UNSUBSCRIBE', [$this->escape($mailbox)], self::COMMAND_NORESPONSE);
 
         return $result == self::ERROR_OK;
     }
@@ -1384,7 +1425,7 @@
      */
     public function createFolder($mailbox, $types = null)
     {
-        $args = array($this->escape($mailbox));
+        $args = [$this->escape($mailbox)];
 
         // RFC 6154: CREATE-SPECIAL-USE
         if (!empty($types) && $this->getCapability('CREATE-SPECIAL-USE')) {
@@ -1399,14 +1440,14 @@
     /**
      * Folder renaming (RENAME)
      *
-     * @param string $mailbox Mailbox name
+     * @param string $from Mailbox name
+     * @param string $to   Mailbox name
      *
      * @return bool True on success, False on error
      */
     public function renameFolder($from, $to)
     {
-        $result = $this->execute('RENAME', array($this->escape($from), $this->escape($to)),
-            self::COMMAND_NORESPONSE);
+        $result = $this->execute('RENAME', [$this->escape($from), $this->escape($to)], self::COMMAND_NORESPONSE);
 
         return $result == self::ERROR_OK;
     }
@@ -1416,12 +1457,16 @@
      *
      * @param string $mailbox Mailbox name
      *
-     * @return boolean True on success, False on error
+     * @return bool True on success, False on error
      */
     public function deleteFolder($mailbox)
     {
-        $result = $this->execute('DELETE', array($this->escape($mailbox)),
-            self::COMMAND_NORESPONSE);
+        // Unselect the folder to prevent "BYE Fatal error: Mailbox has been (re)moved" on Cyrus IMAP
+        if ($this->selected === $mailbox && $this->hasCapability('UNSELECT')) {
+            $this->execute('UNSELECT', [], self::COMMAND_NORESPONSE);
+        }
+
+        $result = $this->execute('DELETE', [$this->escape($mailbox)], self::COMMAND_NORESPONSE);
 
         return $result == self::ERROR_OK;
     }
@@ -1431,25 +1476,27 @@
      *
      * @param string $mailbox Mailbox name
      *
-     * @return boolean True on success, False on error
+     * @return bool True on success, False on error
      */
     public function clearFolder($mailbox)
     {
-        $res = false;
         if ($this->countMessages($mailbox) > 0) {
             $res = $this->flag($mailbox, '1:*', 'DELETED');
+        } else {
+            return true;
         }
 
-        if ($res) {
+        if (!empty($res)) {
             if ($this->selected === $mailbox) {
                 $res = $this->close();
-            }
-            else {
+            } else {
                 $res = $this->expunge($mailbox);
             }
+
+            return $res;
         }
 
-        return $res;
+        return false;
     }
 
     /**
@@ -1460,10 +1507,10 @@
      * @param array  $return_opts (see self::_listMailboxes)
      * @param array  $select_opts (see self::_listMailboxes)
      *
-     * @return array|bool List of mailboxes or hash of options if STATUS/MYROGHTS response
+     * @return array|bool List of mailboxes or hash of options if STATUS/MYRIGHTS response
      *                    is requested, False on error.
      */
-    public function listMailboxes($ref, $mailbox, $return_opts = array(), $select_opts = array())
+    public function listMailboxes($ref, $mailbox, $return_opts = [], $select_opts = [])
     {
         return $this->_listMailboxes($ref, $mailbox, false, $return_opts, $select_opts);
     }
@@ -1475,10 +1522,10 @@
      * @param string $mailbox     Mailbox name
      * @param array  $return_opts (see self::_listMailboxes)
      *
-     * @return array|bool List of mailboxes or hash of options if STATUS/MYROGHTS response
+     * @return array|bool List of mailboxes or hash of options if STATUS/MYRIGHTS response
      *                    is requested, False on error.
      */
-    public function listSubscribed($ref, $mailbox, $return_opts = array())
+    public function listSubscribed($ref, $mailbox, $return_opts = [])
     {
         return $this->_listMailboxes($ref, $mailbox, true, $return_opts, null);
     }
@@ -1491,23 +1538,23 @@
      * @param bool   $subscribed  Enables returning subscribed mailboxes only
      * @param array  $return_opts List of RETURN options (RFC5819: LIST-STATUS, RFC5258: LIST-EXTENDED)
      *                            Possible: MESSAGES, RECENT, UIDNEXT, UIDVALIDITY, UNSEEN,
-     *                                      MYRIGHTS, SUBSCRIBED, CHILDREN
+     *                            MYRIGHTS, SUBSCRIBED, CHILDREN
      * @param array  $select_opts List of selection options (RFC5258: LIST-EXTENDED)
      *                            Possible: SUBSCRIBED, RECURSIVEMATCH, REMOTE,
-     *                                      SPECIAL-USE (RFC6154)
+     *                            SPECIAL-USE (RFC6154)
      *
-     * @return array|bool List of mailboxes or hash of options if STATUS/MYROGHTS response
+     * @return array|bool List of mailboxes or hash of options if STATUS/MYRIGHTS response
      *                    is requested, False on error.
      */
-    protected function _listMailboxes($ref, $mailbox, $subscribed=false,
-        $return_opts=array(), $select_opts=array())
+    protected function _listMailboxes($ref, $mailbox, $subscribed = false, $return_opts = [], $select_opts = [])
     {
         if (!strlen($mailbox)) {
             $mailbox = '*';
         }
 
-        $args = array();
-        $rets = array();
+        $lstatus = false;
+        $args    = [];
+        $rets    = [];
 
         if (!empty($select_opts) && $this->getCapability('LIST-EXTENDED')) {
             $select_opts = (array) $select_opts;
@@ -1515,20 +1562,18 @@
             $args[] = '(' . implode(' ', $select_opts) . ')';
         }
 
-        $lstatus = false;
-
         $args[] = $this->escape($ref);
         $args[] = $this->escape($mailbox);
 
         if (!empty($return_opts) && $this->getCapability('LIST-EXTENDED')) {
-            $ext_opts    = array('SUBSCRIBED', 'CHILDREN');
+            $ext_opts    = ['SUBSCRIBED', 'CHILDREN'];
             $rets        = array_intersect($return_opts, $ext_opts);
             $return_opts = array_diff($return_opts, $rets);
         }
 
         if (!empty($return_opts) && $this->getCapability('LIST-STATUS')) {
             $lstatus     = true;
-            $status_opts = array('MESSAGES', 'RECENT', 'UIDNEXT', 'UIDVALIDITY', 'UNSEEN');
+            $status_opts = ['MESSAGES', 'RECENT', 'UIDNEXT', 'UIDVALIDITY', 'UNSEEN', 'SIZE'];
             $opts        = array_diff($return_opts, $status_opts);
             $status_opts = array_diff($return_opts, $opts);
 
@@ -1545,17 +1590,17 @@
             $args[] = 'RETURN (' . implode(' ', $rets) . ')';
         }
 
-        list($code, $response) = $this->execute($subscribed ? 'LSUB' : 'LIST', $args);
+        [$code, $response] = $this->execute($subscribed ? 'LSUB' : 'LIST', $args);
 
         if ($code == self::ERROR_OK) {
-            $folders  = array();
+            $folders  = [];
             $last     = 0;
             $pos      = 0;
             $response .= "\r\n";
 
-            while ($pos = strpos($response, "\r\n", $pos+1)) {
+            while ($pos = strpos($response, "\r\n", $pos + 1)) {
                 // literal string, not real end-of-command-line
-                if ($response[$pos-1] == '}') {
+                if ($response[$pos - 1] == '}') {
                     continue;
                 }
 
@@ -1571,19 +1616,30 @@
 
                 // * LIST (<options>) <delimiter> <mailbox>
                 if ($cmd == 'LIST' || $cmd == 'LSUB') {
-                    list($opts, $delim, $mailbox) = $this->tokenizeResponse($line, 3);
+                    [$opts, $delim, $mailbox] = $this->tokenizeResponse($line, 3);
 
                     // Remove redundant separator at the end of folder name, UW-IMAP bug? (#1488879)
                     if ($delim) {
                         $mailbox = rtrim($mailbox, $delim);
                     }
 
+                    // Make it easier for the client to deal with INBOX folder
+                    // by always returning the word with all capital letters
+                    if (strlen($mailbox) == 5
+                        && ($mailbox[0] == 'i' || $mailbox[0] == 'I')
+                        && ($mailbox[1] == 'n' || $mailbox[1] == 'N')
+                        && ($mailbox[2] == 'b' || $mailbox[2] == 'B')
+                        && ($mailbox[3] == 'o' || $mailbox[3] == 'O')
+                        && ($mailbox[4] == 'x' || $mailbox[4] == 'X')
+                    ) {
+                        $mailbox = 'INBOX';
+                    }
+
                     // Add to result array
                     if (!$lstatus) {
                         $folders[] = $mailbox;
-                    }
-                    else {
-                        $folders[$mailbox] = array();
+                    } else {
+                        $folders[$mailbox] = [];
                     }
 
                     // store folder options
@@ -1591,26 +1647,24 @@
                         // Add to options array
                         if (empty($this->data['LIST'][$mailbox])) {
                             $this->data['LIST'][$mailbox] = $opts;
-                        }
-                        else if (!empty($opts)) {
+                        } elseif (!empty($opts)) {
                             $this->data['LIST'][$mailbox] = array_unique(array_merge(
                                 $this->data['LIST'][$mailbox], $opts));
                         }
                     }
-                }
-                else if ($lstatus) {
+                } elseif ($lstatus) {
                     // * STATUS <mailbox> (<result>)
                     if ($cmd == 'STATUS') {
-                        list($mailbox, $status) = $this->tokenizeResponse($line, 2);
+                        [$mailbox, $status] = $this->tokenizeResponse($line, 2);
 
-                        for ($i=0, $len=count($status); $i<$len; $i += 2) {
-                            list($name, $value) = $this->tokenizeResponse($status, 2);
+                        for ($i = 0, $len = count($status); $i < $len; $i += 2) {
+                            [$name, $value] = $this->tokenizeResponse($status, 2);
                             $folders[$mailbox][$name] = $value;
                         }
                     }
                     // * MYRIGHTS <mailbox> <acl>
-                    else if ($cmd == 'MYRIGHTS') {
-                        list($mailbox, $acl)  = $this->tokenizeResponse($line, 2);
+                    elseif ($cmd == 'MYRIGHTS') {
+                        [$mailbox, $acl]  = $this->tokenizeResponse($line, 2);
                         $folders[$mailbox]['MYRIGHTS'] = $acl;
                     }
                 }
@@ -1635,9 +1689,10 @@
             return $this->data['EXISTS'];
         }
 
-        if (isset($this->data["STATUS:".$mailbox])) {
-            $cache = $this->data["STATUS:".$mailbox];
-            if (!empty($cache) && isset($cache['MESSAGES'])) {
+        // Check internal cache
+        if (!empty($this->data['STATUS:' . $mailbox])) {
+            $cache = $this->data['STATUS:' . $mailbox];
+            if (isset($cache['MESSAGES'])) {
                 return (int) $cache['MESSAGES'];
             }
         }
@@ -1665,13 +1720,13 @@
         }
 
         // Check internal cache
-        $cache = $this->data['STATUS:'.$mailbox];
+        $cache = $this->data['STATUS:' . $mailbox];
         if (!empty($cache) && isset($cache['RECENT'])) {
             return (int) $cache['RECENT'];
         }
 
         // Try STATUS (should be faster than SELECT)
-        $counts = $this->status($mailbox, array('RECENT'));
+        $counts = $this->status($mailbox, ['RECENT']);
         if (is_array($counts)) {
             return (int) $counts['RECENT'];
         }
@@ -1689,9 +1744,11 @@
     public function countUnseen($mailbox)
     {
         // Check internal cache
-        $cache = $this->data['STATUS:'.$mailbox];
-        if (!empty($cache) && isset($cache['UNSEEN'])) {
-            return (int) $cache['UNSEEN'];
+        if (!empty($this->data['STATUS:' . $mailbox])) {
+            $cache = $this->data['STATUS:' . $mailbox];
+            if (isset($cache['UNSEEN'])) {
+                return (int) $cache['UNSEEN'];
+            }
         }
 
         // Try STATUS (should be faster than SELECT+SEARCH)
@@ -1701,7 +1758,7 @@
         }
 
         // Invoke SEARCH as a fallback
-        $index = $this->search($mailbox, 'ALL UNSEEN', false, array('COUNT'));
+        $index = $this->search($mailbox, 'ALL UNSEEN', false, ['COUNT']);
         if (!$index->is_error()) {
             return $index->count();
         }
@@ -1714,10 +1771,11 @@
      *
      * @param array $items Client identification information key/value hash
      *
-     * @return array Server identification information key/value hash
+     * @return array|false Server identification information key/value hash, False on error
+     *
      * @since 0.6
      */
-    public function id($items = array())
+    public function id($items = [])
     {
         if (is_array($items) && !empty($items)) {
             foreach ($items as $key => $value) {
@@ -1726,17 +1784,20 @@
             }
         }
 
-        list($code, $response) = $this->execute('ID',
-            array(!empty($args) ? '(' . implode(' ', (array) $args) . ')' : $this->escape(null)),
-            0, '/^\* ID /i');
+        [$code, $response] = $this->execute('ID',
+            [!empty($args) ? '(' . implode(' ', (array) $args) . ')' : $this->escape(null)],
+            0, '/^\* ID /i'
+        );
 
         if ($code == self::ERROR_OK && $response) {
             $response = substr($response, 5); // remove prefix "* ID "
             $items    = $this->tokenizeResponse($response, 1);
-            $result   = null;
+            $result   = [];
 
-            for ($i=0, $len=count($items); $i<$len; $i += 2) {
-                $result[$items[$i]] = $items[$i+1];
+            if (is_array($items)) {
+                for ($i = 0, $len = count($items); $i < $len; $i += 2) {
+                    $result[$items[$i]] = $items[$i + 1];
+                }
             }
 
             return $result;
@@ -1751,6 +1812,7 @@
      * @param mixed $extension Extension name to enable (or array of names)
      *
      * @return array|bool List of enabled extensions, False on error
+     *
      * @since 0.6
      */
     public function enable($extension)
@@ -1764,7 +1826,7 @@
         }
 
         if (!is_array($extension)) {
-            $extension = array($extension);
+            $extension = [$extension];
         }
 
         if (!empty($this->extensions_enabled)) {
@@ -1781,13 +1843,13 @@
             }
         }
 
-        list($code, $response) = $this->execute('ENABLE', $extension, 0, '/^\* ENABLED /i');
+        [$code, $response] = $this->execute('ENABLE', $extension, 0, '/^\* ENABLED /i');
 
         if ($code == self::ERROR_OK && $response) {
             $response = substr($response, 10); // remove prefix "* ENABLED "
             $result   = (array) $this->tokenizeResponse($response);
 
-            $this->extensions_enabled = array_unique(array_merge((array)$this->extensions_enabled, $result));
+            $this->extensions_enabled = array_unique(array_merge((array) $this->extensions_enabled, $result));
 
             return $this->extensions_enabled;
         }
@@ -1809,7 +1871,7 @@
     public function sort($mailbox, $field = 'ARRIVAL', $criteria = '', $return_uid = false, $encoding = 'US-ASCII')
     {
         $old_sel   = $this->selected;
-        $supported = array('ARRIVAL', 'CC', 'DATE', 'FROM', 'SIZE', 'SUBJECT', 'TO');
+        $supported = ['ARRIVAL', 'CC', 'DATE', 'FROM', 'SIZE', 'SUBJECT', 'TO'];
         $field     = strtoupper($field);
 
         if ($field == 'INTERNALDATE') {
@@ -1825,7 +1887,7 @@
         }
 
         // return empty result when folder is empty and we're just after SELECT
-        if ($old_sel != $mailbox && !$this->data['EXISTS']) {
+        if ($old_sel != $mailbox && empty($this->data['EXISTS'])) {
             return new rcube_result_index($mailbox, '* SORT');
         }
 
@@ -1837,8 +1899,8 @@
         $encoding = $encoding ? trim($encoding) : 'US-ASCII';
         $criteria = $criteria ? 'ALL ' . trim($criteria) : 'ALL';
 
-        list($code, $response) = $this->execute($return_uid ? 'UID SORT' : 'SORT',
-            array("($field)", $encoding, $criteria));
+        [$code, $response] = $this->execute($return_uid ? 'UID SORT' : 'SORT',
+            ["($field)", $encoding, $criteria]);
 
         if ($code != self::ERROR_OK) {
             $response = null;
@@ -1873,10 +1935,10 @@
 
         $encoding  = $encoding ? trim($encoding) : 'US-ASCII';
         $algorithm = $algorithm ? trim($algorithm) : 'REFERENCES';
-        $criteria  = $criteria ? 'ALL '.trim($criteria) : 'ALL';
+        $criteria  = $criteria ? 'ALL ' . trim($criteria) : 'ALL';
 
-        list($code, $response) = $this->execute($return_uid ? 'UID THREAD' : 'THREAD',
-            array($algorithm, $encoding, $criteria));
+        [$code, $response] = $this->execute($return_uid ? 'UID THREAD' : 'THREAD',
+            [$algorithm, $encoding, $criteria]);
 
         if ($code != self::ERROR_OK) {
             $response = null;
@@ -1895,7 +1957,7 @@
      *
      * @return rcube_result_index Result data
      */
-    public function search($mailbox, $criteria, $return_uid = false, $items = array())
+    public function search($mailbox, $criteria, $return_uid = false, $items = [])
     {
         $old_sel = $this->selected;
 
@@ -1911,7 +1973,7 @@
         // If ESEARCH is supported always use ALL
         // but not when items are specified or using simple id2uid search
         if (empty($items) && preg_match('/[^0-9]/', $criteria)) {
-            $items = array('ALL');
+            $items = ['ALL'];
         }
 
         $esearch  = empty($items) ? false : $this->getCapability('ESEARCH');
@@ -1925,13 +1987,11 @@
 
         if (!empty($criteria)) {
             $params .= ($params ? ' ' : '') . $criteria;
-        }
-        else {
+        } else {
             $params .= 'ALL';
         }
 
-        list($code, $response) = $this->execute($return_uid ? 'UID SEARCH' : 'SEARCH',
-            array($params));
+        [$code, $response] = $this->execute($return_uid ? 'UID SEARCH' : 'SEARCH', [$params]);
 
         if ($code != self::ERROR_OK) {
             $response = null;
@@ -1952,8 +2012,8 @@
      *
      * @return rcube_result_index Response data
      */
-    public function index($mailbox, $message_set, $index_field='', $skip_deleted=true,
-        $uidfetch=false, $return_uid=false)
+    public function index($mailbox, $message_set, $index_field = '', $skip_deleted = true,
+        $uidfetch = false, $return_uid = false)
     {
         $msg_index = $this->fetchHeaderIndex($mailbox, $message_set,
             $index_field, $skip_deleted, $uidfetch, $return_uid);
@@ -1962,8 +2022,7 @@
             asort($msg_index); // ASC
             $msg_index = array_keys($msg_index);
             $msg_index = '* SEARCH ' . implode(' ', $msg_index);
-        }
-        else {
+        } else {
             $msg_index = is_array($msg_index) ? '* SEARCH' : null;
         }
 
@@ -1985,41 +2044,45 @@
     public function fetchHeaderIndex($mailbox, $message_set, $index_field = '', $skip_deleted = true,
         $uidfetch = false, $return_uid = false)
     {
+        // Validate input
         if (is_array($message_set)) {
             if (!($message_set = $this->compressMessageSet($message_set))) {
                 return false;
             }
-        }
-        else {
-            list($from_idx, $to_idx) = explode(':', $message_set);
-            if (empty($message_set) ||
-                (isset($to_idx) && $to_idx != '*' && (int)$from_idx > (int)$to_idx)
-            ) {
+        } elseif (empty($message_set)) {
+            return false;
+        } elseif (strpos($message_set, ':')) {
+            [$from_idx, $to_idx] = explode(':', $message_set);
+            if ($to_idx != '*' && (int) $from_idx > (int) $to_idx) {
                 return false;
             }
         }
 
         $index_field = empty($index_field) ? 'DATE' : strtoupper($index_field);
 
-        $fields_a['DATE']         = 1;
-        $fields_a['INTERNALDATE'] = 4;
-        $fields_a['ARRIVAL']      = 4;
-        $fields_a['FROM']         = 1;
-        $fields_a['REPLY-TO']     = 1;
-        $fields_a['SENDER']       = 1;
-        $fields_a['TO']           = 1;
-        $fields_a['CC']           = 1;
-        $fields_a['SUBJECT']      = 1;
-        $fields_a['UID']          = 2;
-        $fields_a['SIZE']         = 2;
-        $fields_a['SEEN']         = 3;
-        $fields_a['RECENT']       = 3;
-        $fields_a['DELETED']      = 3;
-
-        if (!($mode = $fields_a[$index_field])) {
+        $supported = [
+            'DATE'         => 1,
+            'INTERNALDATE' => 4,
+            'ARRIVAL'      => 4,
+            'FROM'         => 1,
+            'REPLY-TO'     => 1,
+            'SENDER'       => 1,
+            'TO'           => 1,
+            'CC'           => 1,
+            'SUBJECT'      => 1,
+            'UID'          => 2,
+            'SIZE'         => 2,
+            'SEEN'         => 3,
+            'RECENT'       => 3,
+            'DELETED'      => 3,
+        ];
+
+        if (empty($supported[$index_field])) {
             return false;
         }
 
+        $mode = $supported[$index_field];
+
         //  Select the mailbox
         if (!$this->select($mailbox)) {
             return false;
@@ -2028,7 +2091,7 @@
         // build FETCH command string
         $key    = $this->nextTag();
         $cmd    = $uidfetch ? 'UID FETCH' : 'FETCH';
-        $fields = array();
+        $fields = [];
 
         if ($return_uid) {
             $fields[] = 'UID';
@@ -2042,30 +2105,26 @@
                 $fields[] = 'INTERNALDATE';
             }
             $fields[] = "BODY.PEEK[HEADER.FIELDS ($index_field)]";
-        }
-        else if ($mode == 2) {
+        } elseif ($mode == 2) {
             if ($index_field == 'SIZE') {
                 $fields[] = 'RFC822.SIZE';
-            }
-            else if (!$return_uid || $index_field != 'UID') {
+            } elseif (!$return_uid || $index_field != 'UID') {
                 $fields[] = $index_field;
             }
-        }
-        else if ($mode == 3 && !$skip_deleted) {
+        } elseif ($mode == 3 && !$skip_deleted) {
             $fields[] = 'FLAGS';
-        }
-        else if ($mode == 4) {
+        } elseif ($mode == 4) {
             $fields[] = 'INTERNALDATE';
         }
 
-        $request = "$key $cmd $message_set (" . implode(' ', $fields) . ")";
+        $request = "$key $cmd $message_set (" . implode(' ', $fields) . ')';
 
         if (!$this->putLine($request)) {
             $this->setError(self::ERROR_COMMAND, "Failed to send $cmd command");
             return false;
         }
 
-        $result = array();
+        $result = [];
 
         do {
             $line = rtrim($this->readLine(200));
@@ -2078,11 +2137,11 @@
                 if ($return_uid) {
                     if (preg_match('/UID ([0-9]+)/', $line, $matches)) {
                         $id = (int) $matches[1];
-                    }
-                    else {
+                    } else {
                         continue;
                     }
                 }
+
                 if ($skip_deleted && preg_match('/FLAGS \(([^)]+)\)/', $line, $matches)) {
                     $flags = explode(' ', strtoupper($matches[1]));
                     if (in_array('\\DELETED', $flags)) {
@@ -2092,7 +2151,7 @@
 
                 if ($mode == 1 && $index_field == 'DATE') {
                     if (preg_match('/BODY\[HEADER\.FIELDS \("*DATE"*\)\] (.*)/', $line, $matches)) {
-                        $value = preg_replace(array('/^"*[a-z]+:/i'), '', $matches[1]);
+                        $value = preg_replace(['/^"*[a-z]+:/i'], '', $matches[1]);
                         $value = trim($value);
                         $result[$id] = rcube_utils::strtotime($value);
                     }
@@ -2100,46 +2159,37 @@
                     if (empty($result[$id])) {
                         if (preg_match('/INTERNALDATE "([^"]+)"/', $line, $matches)) {
                             $result[$id] = rcube_utils::strtotime($matches[1]);
-                        }
-                        else {
+                        } else {
                             $result[$id] = 0;
                         }
                     }
-                }
-                else if ($mode == 1) {
+                } elseif ($mode == 1) {
                     if (preg_match('/BODY\[HEADER\.FIELDS \("?(FROM|REPLY-TO|SENDER|TO|SUBJECT)"?\)\] (.*)/', $line, $matches)) {
-                        $value = preg_replace(array('/^"*[a-z]+:/i', '/\s+$/sm'), array('', ''), $matches[2]);
+                        $value = preg_replace(['/^"*[a-z]+:/i', '/\s+$/sm'], ['', ''], $matches[2]);
                         $result[$id] = trim($value);
-                    }
-                    else {
+                    } else {
                         $result[$id] = '';
                     }
-                }
-                else if ($mode == 2) {
+                } elseif ($mode == 2) {
                     if (preg_match('/' . $index_field . ' ([0-9]+)/', $line, $matches)) {
                         $result[$id] = trim($matches[1]);
-                    }
-                    else {
+                    } else {
                         $result[$id] = 0;
                     }
-                }
-                else if ($mode == 3) {
+                } elseif ($mode == 3) {
                     if (!$flags && preg_match('/FLAGS \(([^)]+)\)/', $line, $matches)) {
                         $flags = explode(' ', $matches[1]);
                     }
-                    $result[$id] = in_array("\\".$index_field, (array) $flags) ? 1 : 0;
-                }
-                else if ($mode == 4) {
+                    $result[$id] = in_array('\\' . $index_field, (array) $flags) ? 1 : 0;
+                } elseif ($mode == 4) {
                     if (preg_match('/INTERNALDATE "([^"]+)"/', $line, $matches)) {
                         $result[$id] = rcube_utils::strtotime($matches[1]);
-                    }
-                    else {
+                    } else {
                         $result[$id] = 0;
                     }
                 }
             }
-        }
-        while (!$this->startsWith($line, $key, true, true));
+        } while (!$this->startsWith($line, $key, true, true));
 
         return $result;
     }
@@ -2168,7 +2218,7 @@
      * Returns message unique identifier (UID)
      *
      * @param string $mailbox Mailbox name
-     * @param int    $uid     Message sequence identifier
+     * @param int    $id      Message sequence identifier
      *
      * @return int Message unique identifier
      */
@@ -2182,8 +2232,8 @@
             return null;
         }
 
-        if ($uid = $this->data['UID-MAP'][$id]) {
-            return $uid;
+        if (!empty($this->data['UID-MAP'][$id])) {
+            return $this->data['UID-MAP'][$id];
         }
 
         if (isset($this->data['EXISTS']) && $id > $this->data['EXISTS']) {
@@ -2246,12 +2296,12 @@
             return false;
         }
 
-        if (!$this->data['READ-WRITE']) {
-            $this->setError(self::ERROR_READONLY, "Mailbox is read-only");
+        if (empty($this->data['READ-WRITE'])) {
+            $this->setError(self::ERROR_READONLY, 'Mailbox is read-only');
             return false;
         }
 
-        if ($this->flags[strtoupper($flag)]) {
+        if (!empty($this->flags[strtoupper($flag)])) {
             $flag = $this->flags[strtoupper($flag)];
         }
 
@@ -2265,16 +2315,17 @@
 
         // Clear internal status cache
         if ($flag == 'SEEN') {
-            unset($this->data['STATUS:'.$mailbox]['UNSEEN']);
+            unset($this->data['STATUS:' . $mailbox]['UNSEEN']);
         }
 
         if ($mod != '+' && $mod != '-') {
             $mod = '+';
         }
 
-        $result = $this->execute('UID STORE', array(
-            $this->compressMessageSet($messages), $mod . 'FLAGS.SILENT', "($flag)"),
-            self::COMMAND_NORESPONSE);
+        $result = $this->execute('UID STORE',
+            [$this->compressMessageSet($messages), $mod . 'FLAGS.SILENT', "($flag)"],
+            self::COMMAND_NORESPONSE
+        );
 
         return $result == self::ERROR_OK;
     }
@@ -2298,11 +2349,12 @@
         }
 
         // Clear internal status cache
-        unset($this->data['STATUS:'.$to]);
+        unset($this->data['STATUS:' . $to]);
 
-        $result = $this->execute('UID COPY', array(
-            $this->compressMessageSet($messages), $this->escape($to)),
-            self::COMMAND_NORESPONSE);
+        $result = $this->execute('UID COPY',
+            [$this->compressMessageSet($messages), $this->escape($to)],
+            self::COMMAND_NORESPONSE
+        );
 
         return $result == self::ERROR_OK;
     }
@@ -2322,8 +2374,8 @@
             return false;
         }
 
-        if (!$this->data['READ-WRITE']) {
-            $this->setError(self::ERROR_READONLY, "Mailbox is read-only");
+        if (empty($this->data['READ-WRITE'])) {
+            $this->setError(self::ERROR_READONLY, 'Mailbox is read-only');
             return false;
         }
 
@@ -2333,12 +2385,13 @@
             unset($this->data['COPYUID']);
 
             // Clear internal status cache
-            unset($this->data['STATUS:'.$to]);
+            unset($this->data['STATUS:' . $to]);
             $this->clear_status_cache($from);
 
-            $result = $this->execute('UID MOVE', array(
-                $this->compressMessageSet($messages), $this->escape($to)),
-                self::COMMAND_NORESPONSE);
+            $result = $this->execute('UID MOVE',
+                [$this->compressMessageSet($messages), $this->escape($to)],
+                self::COMMAND_NORESPONSE
+            );
 
             return $result == self::ERROR_OK;
         }
@@ -2348,15 +2401,14 @@
 
         if ($result) {
             // Clear internal status cache
-            unset($this->data['STATUS:'.$from]);
+            unset($this->data['STATUS:' . $from]);
 
             $result = $this->flag($from, $messages, 'DELETED');
 
             if ($messages == '*') {
                 // CLOSE+SELECT should be faster than EXPUNGE
                 $this->close();
-            }
-            else {
+            } else {
                 $this->expunge($from, $messages);
             }
         }
@@ -2375,9 +2427,10 @@
      * @param bool   $vanished    Enables VANISHED parameter (RFC5162) for CHANGEDSINCE query
      *
      * @return array List of rcube_message_header elements, False on error
+     *
      * @since 0.6
      */
-    public function fetch($mailbox, $message_set, $is_uid = false, $query_items = array(),
+    public function fetch($mailbox, $message_set, $is_uid = false, $query_items = [],
         $mod_seq = null, $vanished = false)
     {
         if (!$this->select($mailbox)) {
@@ -2385,14 +2438,14 @@
         }
 
         $message_set = $this->compressMessageSet($message_set);
-        $result      = array();
+        $result      = [];
 
         $key      = $this->nextTag();
         $cmd      = ($is_uid ? 'UID ' : '') . 'FETCH';
-        $request  = "$key $cmd $message_set (" . implode(' ', $query_items) . ")";
+        $request  = "$key $cmd $message_set (" . implode(' ', $query_items) . ')';
 
         if ($mod_seq !== null && $this->hasCapability('CONDSTORE')) {
-            $request .= " (CHANGEDSINCE $mod_seq" . ($vanished ? " VANISHED" : '') .")";
+            $request .= " (CHANGEDSINCE $mod_seq" . ($vanished ? ' VANISHED' : '') . ')';
         }
 
         if (!$this->putLine($request)) {
@@ -2401,7 +2454,7 @@
         }
 
         do {
-            $line = $this->readLine(4096);
+            $line = $this->readFullLine(4096);
 
             if (!$line) {
                 break;
@@ -2415,90 +2468,57 @@
             if (preg_match('/^\* ([0-9]+) FETCH/', $line, $m)) {
                 $id = intval($m[1]);
 
-                $result[$id]            = new rcube_message_header;
+                $result[$id]            = new rcube_message_header();
                 $result[$id]->id        = $id;
                 $result[$id]->subject   = '';
                 $result[$id]->messageID = 'mid:' . $id;
 
                 $headers = null;
-                $lines   = array();
                 $line    = substr($line, strlen($m[0]) + 2);
-                $ln      = 0;
-
-                // get complete entry
-                while (preg_match('/\{([0-9]+)\}\r\n$/', $line, $m)) {
-                    $bytes = $m[1];
-                    $out   = '';
-
-                    while (strlen($out) < $bytes) {
-                        $out = $this->readBytes($bytes);
-                        if ($out === null) {
-                            break;
-                        }
-                        $line .= $out;
-                    }
-
-                    $str = $this->readLine(4096);
-                    if ($str === false) {
-                        break;
-                    }
-
-                    $line .= $str;
-                }
 
                 // Tokenize response and assign to object properties
-                while (list($name, $value) = $this->tokenizeResponse($line, 2)) {
+                while (($tokens = $this->tokenizeResponse($line, 2)) && count($tokens) == 2) {
+                    [$name, $value] = $tokens;
                     if ($name == 'UID') {
                         $result[$id]->uid = intval($value);
-                    }
-                    else if ($name == 'RFC822.SIZE') {
+                    } elseif ($name == 'RFC822.SIZE') {
                         $result[$id]->size = intval($value);
-                    }
-                    else if ($name == 'RFC822.TEXT') {
+                    } elseif ($name == 'RFC822.TEXT') {
                         $result[$id]->body = $value;
-                    }
-                    else if ($name == 'INTERNALDATE') {
+                    } elseif ($name == 'INTERNALDATE') {
                         $result[$id]->internaldate = $value;
                         $result[$id]->date         = $value;
                         $result[$id]->timestamp    = rcube_utils::strtotime($value);
-                    }
-                    else if ($name == 'FLAGS') {
+                    } elseif ($name == 'FLAGS') {
                         if (!empty($value)) {
-                            foreach ((array)$value as $flag) {
-                                $flag = str_replace(array('$', "\\"), '', $flag);
+                            foreach ((array) $value as $flag) {
+                                $flag = str_replace(['$', '\\'], '', $flag);
                                 $flag = strtoupper($flag);
 
                                 $result[$id]->flags[$flag] = true;
                             }
                         }
-                    }
-                    else if ($name == 'MODSEQ') {
+                    } elseif ($name == 'MODSEQ') {
                         $result[$id]->modseq = $value[0];
-                    }
-                    else if ($name == 'ENVELOPE') {
+                    } elseif ($name == 'ENVELOPE') {
                         $result[$id]->envelope = $value;
-                    }
-                    else if ($name == 'BODYSTRUCTURE' || ($name == 'BODY' && count($value) > 2)) {
+                    } elseif ($name == 'BODYSTRUCTURE' || ($name == 'BODY' && count($value) > 2)) {
                         if (!is_array($value[0]) && (strtolower($value[0]) == 'message' && strtolower($value[1]) == 'rfc822')) {
-                            $value = array($value);
+                            $value = [$value];
                         }
                         $result[$id]->bodystructure = $value;
-                    }
-                    else if ($name == 'RFC822') {
+                    } elseif ($name == 'RFC822') {
                         $result[$id]->body = $value;
-                    }
-                    else if (stripos($name, 'BODY[') === 0) {
+                    } elseif (stripos($name, 'BODY[') === 0) {
                         $name = str_replace(']', '', substr($name, 5));
 
                         if ($name == 'HEADER.FIELDS') {
                             // skip ']' after headers list
                             $this->tokenizeResponse($line, 1);
                             $headers = $this->tokenizeResponse($line, 1);
-                        }
-                        else if (strlen($name)) {
+                        } elseif (strlen($name)) {
                             $result[$id]->bodypart[$name] = $value;
-                        }
-                        else {
+                        } else {
                             $result[$id]->body = $value;
                         }
                     }
@@ -2507,89 +2527,97 @@
                 // create array with header field:data
                 if (!empty($headers)) {
                     $headers = explode("\n", trim($headers));
+                    $lines   = [];
+                    $ln      = 0;
+
                     foreach ($headers as $resln) {
-                        if (ord($resln[0]) <= 32) {
-                            $lines[$ln] .= (empty($lines[$ln]) ? '' : "\n") . trim($resln);
-                        }
-                        else {
+                        if (!isset($resln[0]) || ord($resln[0]) <= 32) {
+                            $lines[$ln] = ($lines[$ln] ?? '') . (empty($lines[$ln]) ? '' : "\n") . trim($resln);
+                        } else {
                             $lines[++$ln] = trim($resln);
                         }
                     }
 
                     foreach ($lines as $str) {
-                        list($field, $string) = explode(':', $str, 2);
+                        if (strpos($str, ':') === false) {
+                            continue;
+                        }
+
+                        [$field, $string] = explode(':', $str, 2);
 
                         $field  = strtolower($field);
                         $string = preg_replace('/\n[\t\s]*/', ' ', trim($string));
 
                         switch ($field) {
-                        case 'date';
-                            $string                 = substr($string, 0, 128);
-                            $result[$id]->date      = $string;
-                            $result[$id]->timestamp = rcube_utils::strtotime($string);
-                            break;
-                        case 'to':
-                            $result[$id]->to = preg_replace('/undisclosed-recipients:[;,]*/', '', $string);
-                            break;
-                        case 'from':
-                        case 'subject':
-                            $string = substr($string, 0, 2048);
-                        case 'cc':
-                        case 'bcc':
-                        case 'references':
-                            $result[$id]->{$field} = $string;
-                            break;
-                        case 'reply-to':
-                            $result[$id]->replyto = $string;
-                            break;
-                        case 'content-transfer-encoding':
-                            $result[$id]->encoding = substr($string, 0, 32);
-                        break;
-                        case 'content-type':
-                            $ctype_parts = preg_split('/[; ]+/', $string);
-                            $result[$id]->ctype = strtolower(array_shift($ctype_parts));
-                            if (preg_match('/charset\s*=\s*"?([a-z0-9\-\.\_]+)"?/i', $string, $regs)) {
-                                $result[$id]->charset = $regs[1];
-                            }
-                            break;
-                        case 'in-reply-to':
-                            $result[$id]->in_reply_to = str_replace(array("\n", '<', '>'), '', $string);
-                            break;
-                        case 'return-receipt-to':
-                        case 'disposition-notification-to':
-                        case 'x-confirm-reading-to':
-                            $result[$id]->mdn_to = substr($string, 0, 2048);
-                            break;
-                        case 'message-id':
-                            $result[$id]->messageID = substr($string, 0, 2048);
-                            break;
-                        case 'x-priority':
-                            if (preg_match('/^(\d+)/', $string, $matches)) {
-                                $result[$id]->priority = intval($matches[1]);
-                            }
-                            break;
-                        default:
-                            if (strlen($field) < 3) {
+                            case 'date':
+                                $string                 = substr($string, 0, 128);
+                                $result[$id]->date      = $string;
+                                $result[$id]->timestamp = rcube_utils::strtotime($string);
                                 break;
-                            }
-                            if ($result[$id]->others[$field]) {
-                                $string = array_merge((array)$result[$id]->others[$field], (array)$string);
-                            }
-                            $result[$id]->others[$field] = $string;
+                            case 'to':
+                                $result[$id]->to = preg_replace('/undisclosed-recipients:[;,]*/', '', $string);
+                                break;
+                            case 'from':
+                            case 'subject':
+                                $string = substr($string, 0, 2048);
+                            case 'cc':
+                            case 'bcc':
+                            case 'references':
+                                $result[$id]->{$field} = $string;
+                                break;
+                            case 'reply-to':
+                                $result[$id]->replyto = $string;
+                                break;
+                            case 'content-transfer-encoding':
+                                $result[$id]->encoding = substr($string, 0, 32);
+                                break;
+                            case 'content-type':
+                                $ctype_parts = preg_split('/[; ]+/', $string);
+                                $result[$id]->ctype = strtolower(array_first($ctype_parts));
+                                if (preg_match('/charset\s*=\s*"?([a-z0-9\-\.\_]+)"?/i', $string, $regs)) {
+                                    $result[$id]->charset = $regs[1];
+                                }
+                                break;
+                            case 'in-reply-to':
+                                $result[$id]->in_reply_to = str_replace(["\n", '<', '>'], '', $string);
+                                break;
+                            case 'disposition-notification-to':
+                            case 'x-confirm-reading-to':
+                                $result[$id]->mdn_to = substr($string, 0, 2048);
+                                break;
+                            case 'message-id':
+                                $result[$id]->messageID = substr($string, 0, 2048);
+                                break;
+                            case 'x-priority':
+                                if (preg_match('/^(\d+)/', $string, $matches)) {
+                                    $result[$id]->priority = intval($matches[1]);
+                                }
+                                break;
+                            default:
+                                if (strlen($field) < 3) {
+                                    break;
+                                }
+                                if (!empty($result[$id]->others[$field])) {
+                                    $string = array_merge((array) $result[$id]->others[$field], (array) $string);
+                                }
+                                $result[$id]->others[$field] = $string;
                         }
                     }
                 }
             }
             // VANISHED response (QRESYNC RFC5162)
             // Sample: * VANISHED (EARLIER) 300:310,405,411
-            else if (preg_match('/^\* VANISHED [()EARLIER]*/i', $line, $match)) {
+            elseif (preg_match('/^\* VANISHED [()EARLIER]*/i', $line, $match)) {
                 $line   = substr($line, strlen($match[0]));
                 $v_data = $this->tokenizeResponse($line, 1);
 
                 $this->data['VANISHED'] = $v_data;
             }
+        } while (!$this->startsWith($line, $key, true));
+
+        if ($this->parseResult($line, 'FETCH: ') != self::ERROR_OK) {
+            return false;
         }
-        while (!$this->startsWith($line, $key, true));
 
         return $result;
     }
@@ -2605,11 +2633,11 @@
      *
      * @return bool|array List of rcube_message_header elements, False on error
      */
-    public function fetchHeaders($mailbox, $message_set, $is_uid = false, $bodystr = false, $add_headers = array())
+    public function fetchHeaders($mailbox, $message_set, $is_uid = false, $bodystr = false, $add_headers = [])
     {
-        $query_items = array('UID', 'RFC822.SIZE', 'FLAGS', 'INTERNALDATE');
-        $headers     = array('DATE', 'FROM', 'TO', 'SUBJECT', 'CONTENT-TYPE', 'CC', 'REPLY-TO',
-            'LIST-POST', 'DISPOSITION-NOTIFICATION-TO', 'X-PRIORITY');
+        $query_items = ['UID', 'RFC822.SIZE', 'FLAGS', 'INTERNALDATE'];
+        $headers     = ['DATE', 'FROM', 'TO', 'SUBJECT', 'CONTENT-TYPE', 'CC', 'REPLY-TO',
+            'LIST-POST', 'DISPOSITION-NOTIFICATION-TO', 'X-PRIORITY'];
 
         if (!empty($add_headers)) {
             $add_headers = array_map('strtoupper', $add_headers);
@@ -2636,11 +2664,12 @@
      *
      * @return bool|rcube_message_header Message data, False on error
      */
-    public function fetchHeader($mailbox, $id, $is_uid = false, $bodystr = false, $add_headers = array())
+    public function fetchHeader($mailbox, $id, $is_uid = false, $bodystr = false, $add_headers = [])
     {
         $a = $this->fetchHeaders($mailbox, $id, $is_uid, $bodystr, $add_headers);
+
         if (is_array($a)) {
-            return array_shift($a);
+            return array_first($a);
         }
 
         return false;
@@ -2651,54 +2680,54 @@
      *
      * @param array  $messages Array of rcube_message_header objects
      * @param string $field    Name of the property to sort by
-     * @param string $flag     Sorting order (ASC|DESC)
+     * @param string $order    Sorting order (ASC|DESC)
      *
      * @return array Sorted input array
      */
-    public static function sortHeaders($messages, $field, $flag)
+    public static function sortHeaders($messages, $field, $order = 'ASC')
     {
         $field = empty($field) ? 'uid' : strtolower($field);
-        $order = empty($flag) ? 'ASC' : strtoupper($flag);
-        $index = array();
+        $order = empty($order) ? 'ASC' : strtoupper($order);
+        $index = [];
 
         reset($messages);
 
         // Create an index
         foreach ($messages as $key => $headers) {
             switch ($field) {
-            case 'arrival':
-                $field = 'internaldate';
-                // no-break
-            case 'date':
-            case 'internaldate':
-            case 'timestamp':
-                $value = rcube_utils::strtotime($headers->$field);
-                if (!$value && $field != 'timestamp') {
-                    $value = $headers->timestamp;
-                }
+                case 'arrival':
+                    $field = 'internaldate';
+                    // no-break
+                case 'date':
+                case 'internaldate':
+                case 'timestamp':
+                    $value = rcube_utils::strtotime($headers->{$field});
+                    if (!$value && $field != 'timestamp') {
+                        $value = $headers->timestamp;
+                    }
 
-                break;
+                    break;
 
-            default:
-                // @TODO: decode header value, convert to UTF-8
-                $value = $headers->$field;
-                if (is_string($value)) {
-                    $value = str_replace('"', '', $value);
+                default:
+                    // @TODO: decode header value, convert to UTF-8
+                    $value = $headers->{$field};
+                    if (is_string($value)) {
+                        $value = str_replace('"', '', $value);
 
-                    if ($field == 'subject') {
-                        $value = preg_replace('/^(Re:\s*|Fwd:\s*|Fw:\s*)+/i', '', $value);
+                        if ($field == 'subject') {
+                            $value = rcube_utils::remove_subject_prefix($value);
+                        }
                     }
-                }
             }
 
             $index[$key] = $value;
         }
 
-        $sort_order = $flag == 'ASC' ? SORT_ASC : SORT_DESC;
-        $sort_flags = SORT_STRING | SORT_FLAG_CASE;
+        $sort_order = $order == 'ASC' ? \SORT_ASC : \SORT_DESC;
+        $sort_flags = \SORT_STRING | \SORT_FLAG_CASE;
 
-        if (in_array($field, array('arrival', 'date', 'internaldate', 'timestamp'))) {
-            $sort_flags = SORT_NUMERIC;
+        if (in_array($field, ['arrival', 'date', 'internaldate', 'timestamp', 'size', 'uid', 'id'])) {
+            $sort_flags = \SORT_NUMERIC;
         }
 
         array_multisort($index, $sort_order, $sort_flags, $messages);
@@ -2712,7 +2741,7 @@
      * @param string $mailbox Mailbox name
      * @param int    $uid     Message UID
      * @param array  $parts   Message part identifiers
-     * @param bool   $mime    Use MIME instad of HEADER
+     * @param bool   $mime    Use MIME instead of HEADER
      *
      * @return array|bool Array containing headers string for each specified body
      *                    False on failure.
@@ -2723,10 +2752,9 @@
             return false;
         }
 
-        $result = false;
         $parts  = (array) $parts;
         $key    = $this->nextTag();
-        $peeks  = array();
+        $peeks  = [];
         $type   = $mime ? 'MIME' : 'HEADER';
 
         // format request
@@ -2738,23 +2766,23 @@
 
         // send request
         if (!$this->putLine($request)) {
-            $this->setError(self::ERROR_COMMAND, "Failed to send UID FETCH command");
+            $this->setError(self::ERROR_COMMAND, 'Failed to send UID FETCH command');
             return false;
         }
 
+        $result = [];
+
         do {
             $line = $this->readLine(1024);
-
             if (preg_match('/^\* [0-9]+ FETCH [0-9UID( ]+/', $line, $m)) {
                 $line = ltrim(substr($line, strlen($m[0])));
-                while (preg_match('/^BODY\[([0-9\.]+)\.'.$type.'\]/', $line, $matches)) {
+                while (preg_match('/^\s*BODY\[([0-9\.]+)\.' . $type . '\]/', $line, $matches)) {
                     $line = substr($line, strlen($matches[0]));
                     $result[$matches[1]] = trim($this->multLine($line));
                     $line = $this->readLine(1024);
                 }
             }
-        }
-        while (!$this->startsWith($line, $key, true));
+        } while (!$this->startsWith($line, $key, true));
 
         return $result;
     }
@@ -2764,7 +2792,7 @@
      */
     public function fetchPartHeader($mailbox, $id, $is_uid = false, $part = null)
     {
-        $part = empty($part) ? 'HEADER' : $part.'.MIME';
+        $part = empty($part) ? 'HEADER' : $part . '.MIME';
 
         return $this->handlePartBody($mailbox, $id, $is_uid, $part);
     }
@@ -2772,35 +2800,37 @@
     /**
      * Fetches body of the specified message part
      */
-    public function handlePartBody($mailbox, $id, $is_uid=false, $part='', $encoding=null, $print=null, $file=null, $formatted=false, $max_bytes=0)
+    public function handlePartBody($mailbox, $id, $is_uid = false, $part = '', $encoding = null, $print = null,
+        $file = null, $formatted = false, $max_bytes = 0)
     {
         if (!$this->select($mailbox)) {
             return false;
         }
 
-        $binary = true;
+        $binary    = true;
+        $initiated = false;
 
         do {
             if (!$initiated) {
                 switch ($encoding) {
-                case 'base64':
-                    $mode = 1;
-                    break;
-                case 'quoted-printable':
-                    $mode = 2;
-                    break;
-                case 'x-uuencode':
-                case 'x-uue':
-                case 'uue':
-                case 'uuencode':
-                    $mode = 3;
-                    break;
-                default:
-                    $mode = 0;
+                    case 'base64':
+                        $mode = 1;
+                        break;
+                    case 'quoted-printable':
+                        $mode = 2;
+                        break;
+                    case 'x-uuencode':
+                    case 'x-uue':
+                    case 'uue':
+                    case 'uuencode':
+                        $mode = 3;
+                        break;
+                    default:
+                        $mode = $formatted ? 4 : 0;
                 }
 
                 // Use BINARY extension when possible (and safe)
-                $binary     = $binary && $mode && preg_match('/^[0-9.]+$/', $part) && $this->hasCapability('BINARY');
+                $binary     = $binary && $mode && preg_match('/^[0-9.]+$/', (string) $part) && $this->hasCapability('BINARY');
                 $fetch_mode = $binary ? 'BINARY' : 'BODY';
                 $partial    = $max_bytes ? sprintf('<0.%d>', $max_bytes) : '';
 
@@ -2847,108 +2877,79 @@
             if ($line[0] == '(' && substr($line, -1) == ')') {
                 // tokenize content inside brackets
                 // the content can be e.g.: (UID 9844 BODY[2.4] NIL)
-                $tokens = $this->tokenizeResponse(preg_replace('/(^\(|\)$)/', '', $line));
+                $line = preg_replace('/(^\(|\)$)/', '', $line);
+                $tokens = $this->tokenizeResponse($line);
 
-                for ($i=0; $i<count($tokens); $i+=2) {
+                for ($i = 0; $i < count($tokens); $i += 2) {
                     if (preg_match('/^(BODY|BINARY)/i', $tokens[$i])) {
-                        $result = $tokens[$i+1];
+                        $result = $tokens[$i + 1];
                         $found  = true;
                         break;
                     }
                 }
 
+                // Cyrus IMAP does not return a NO-response on error, but we can detect it
+                // and fallback to a non-binary fetch (#9097)
+                if ($binary && !$found) {
+                    $binary = $initiated = false;
+                    $line = trim($this->readLine(1024)); // the OK response line
+                    continue;
+                }
+
                 if ($result !== false) {
-                    if ($mode == 1) {
-                        $result = base64_decode($result);
-                    }
-                    else if ($mode == 2) {
-                        $result = quoted_printable_decode($result);
-                    }
-                    else if ($mode == 3) {
-                        $result = convert_uudecode($result);
-                    }
+                    $result = $this->decodeContent($result, $mode, true);
                 }
             }
             // response with string literal
-            else if (preg_match('/\{([0-9]+)\}$/', $line, $m)) {
+            elseif (preg_match('/\{([0-9]+)\}$/', $line, $m)) {
                 $bytes = (int) $m[1];
                 $prev  = '';
                 $found = true;
+                $chunkSize = 1024 * 1024;
 
                 // empty body
                 if (!$bytes) {
                     $result = '';
                 }
-                else while ($bytes > 0) {
-                    $line = $this->readLine(8192);
-
-                    if ($line === null) {
-                        break;
-                    }
+                // An optimal path for a case when we need the body as-is in a string
+                elseif (!$mode && !$file && !$print) {
+                    $result = $this->readBytes($bytes);
+                } else {
+                    while ($bytes > 0) {
+                        $chunk = $this->readBytes($bytes > $chunkSize ? $chunkSize : $bytes);
+
+                        if ($chunk === '') {
+                            break;
+                        }
 
-                    $len = strlen($line);
+                        $len = strlen($chunk);
 
-                    if ($len > $bytes) {
-                        $line = substr($line, 0, $bytes);
-                        $len  = strlen($line);
-                    }
-                    $bytes -= $len;
-
-                    // BASE64
-                    if ($mode == 1) {
-                        $line = preg_replace('|[^a-zA-Z0-9+=/]|', '', $line);
-                        // create chunks with proper length for base64 decoding
-                        $line = $prev.$line;
-                        $length = strlen($line);
-                        if ($length % 4) {
-                            $length = floor($length / 4) * 4;
-                            $prev = substr($line, $length);
-                            $line = substr($line, 0, $length);
-                        }
-                        else {
-                            $prev = '';
-                        }
-                        $line = base64_decode($line);
-                    }
-                    // QUOTED-PRINTABLE
-                    else if ($mode == 2) {
-                        $line = rtrim($line, "\t\r\0\x0B");
-                        $line = quoted_printable_decode($line);
-                    }
-                    // UUENCODE
-                    else if ($mode == 3) {
-                        $line = rtrim($line, "\t\r\n\0\x0B");
-                        if ($line == 'end' || preg_match('/^begin\s+[0-7]+\s+.+$/', $line)) {
-                            continue;
+                        if ($len > $bytes) {
+                            $chunk = substr($chunk, 0, $bytes);
+                            $len = strlen($chunk);
                         }
-                        $line = convert_uudecode($line);
-                    }
-                    // default
-                    else if ($formatted) {
-                        $line = rtrim($line, "\t\r\n\0\x0B") . "\n";
-                    }
+                        $bytes -= $len;
 
-                    if ($file) {
-                        if (fwrite($file, $line) === false) {
-                            break;
+                        $chunk = $this->decodeContent($chunk, $mode, $bytes <= 0, $prev);
+
+                        if ($file) {
+                            if (fwrite($file, $chunk) === false) {
+                                break;
+                            }
+                        } elseif ($print) {
+                            echo $chunk;
+                        } else {
+                            $result .= $chunk;
                         }
                     }
-                    else if ($print) {
-                        echo $line;
-                    }
-                    else {
-                        $result .= $line;
-                    }
                 }
             }
-        }
-        while (!$this->startsWith($line, $key, true) || !$initiated);
+        } while (!$this->startsWith($line, $key, true) || !$initiated);
 
         if ($result !== false) {
             if ($file) {
                 return fwrite($file, $result);
-            }
-            else if ($print) {
+            } elseif ($print) {
                 echo $result;
                 return true;
             }
@@ -2959,6 +2960,104 @@
         return false;
     }
 
+    /**
+     * Decodes a chunk of a message part content from a FETCH response.
+     *
+     * @param string $chunk   Content
+     * @param int    $mode    Encoding mode
+     * @param bool   $is_last Whether it is a last chunk of data
+     * @param string $prev    Extra content from the previous chunk
+     *
+     * @return string Encoded string
+     */
+    protected static function decodeContent($chunk, $mode, $is_last = false, &$prev = '')
+    {
+        // BASE64
+        if ($mode == 1) {
+            $chunk = $prev . preg_replace('|[^a-zA-Z0-9+=/]|', '', $chunk);
+
+            // create chunks with proper length for base64 decoding
+            $length = strlen($chunk);
+
+            if ($length % 4) {
+                $length = floor($length / 4) * 4;
+                $prev = substr($chunk, $length);
+                $chunk = substr($chunk, 0, $length);
+            } else {
+                $prev = '';
+            }
+
+            return base64_decode($chunk);
+        }
+
+        // QUOTED-PRINTABLE
+        if ($mode == 2) {
+            if (!self::decodeContentChunk($chunk, $prev, $is_last)) {
+                return '';
+            }
+
+            $chunk = preg_replace('/[\t\r\0\x0B]+\n/', "\n", $chunk);
+
+            return quoted_printable_decode($chunk);
+        }
+
+        // X-UUENCODE
+        if ($mode == 3) {
+            if (!self::decodeContentChunk($chunk, $prev, $is_last)) {
+                return '';
+            }
+
+            $chunk = preg_replace(
+                ['/\r?\n/', '/(^|\n)end$/', '/^begin\s+[0-7]{3,4}\s+[^\n]+\n/'],
+                ["\n", '', ''],
+                $chunk
+            );
+
+            if (!strlen($chunk)) {
+                return '';
+            }
+
+            return convert_uudecode($chunk);
+        }
+
+        // Plain text formatted
+        // TODO: Formatting should be handled outside of this class
+        if ($mode == 4) {
+            if (!self::decodeContentChunk($chunk, $prev, $is_last)) {
+                return '';
+            }
+
+            if ($is_last) {
+                $chunk = rtrim($chunk, "\t\r\n\0\x0B");
+            }
+
+            return preg_replace('/[\t\r\0\x0B]+\n/', "\n", $chunk);
+        }
+
+        return $chunk;
+    }
+
+    /**
+     * A helper for a new-line aware parsing. See self::decodeContent().
+     */
+    private static function decodeContentChunk(&$chunk, &$prev, $is_last)
+    {
+        $chunk = $prev . $chunk;
+        $prev = '';
+
+        if (!$is_last) {
+            if (($pos = strrpos($chunk, "\n")) !== false) {
+                $prev = substr($chunk, $pos + 1);
+                $chunk = substr($chunk, 0, $pos + 1);
+            } else {
+                $prev = $chunk;
+                return false;
+            }
+        }
+
+        return true;
+    }
+
     /**
      * Handler for IMAP APPEND command
      *
@@ -2970,7 +3069,7 @@
      *
      * @return string|bool On success APPENDUID response (if available) or True, False on failure
      */
-    public function append($mailbox, &$message, $flags = array(), $date = null, $binary = false)
+    public function append($mailbox, &$message, $flags = [], $date = null, $binary = false)
     {
         unset($this->data['APPENDUID']);
 
@@ -2979,20 +3078,19 @@
         }
 
         $binary       = $binary && $this->getCapability('BINARY');
-        $literal_plus = !$binary && $this->prefs['literal+'];
+        $literal_plus = !$binary && !empty($this->prefs['literal+']);
         $len          = 0;
-        $msg          = is_array($message) ? $message : array(&$message);
+        $msg          = is_array($message) ? $message : [&$message];
         $chunk_size   = 512000;
 
-        for ($i=0, $cnt=count($msg); $i<$cnt; $i++) {
+        for ($i = 0, $cnt = count($msg); $i < $cnt; $i++) {
             if (is_resource($msg[$i])) {
                 $stat = fstat($msg[$i]);
                 if ($stat === false) {
                     return false;
                 }
                 $len += $stat['size'];
-            }
-            else {
+            } else {
                 if (!$binary) {
                     $msg[$i] = str_replace("\r", '', $msg[$i]);
                     $msg[$i] = str_replace("\n", "\r\n", $msg[$i]);
@@ -3016,7 +3114,7 @@
 
         // send APPEND command
         if (!$this->putLine($request)) {
-            $this->setError(self::ERROR_COMMAND, "Failed to send APPEND command");
+            $this->setError(self::ERROR_COMMAND, 'Failed to send APPEND command');
             return false;
         }
 
@@ -3064,7 +3162,7 @@
         } while (!$this->startsWith($line, $key, true, true));
 
         // Clear internal status cache
-        unset($this->data['STATUS:'.$mailbox]);
+        unset($this->data['STATUS:' . $mailbox]);
 
         if ($this->parseResult($line, 'APPEND: ') != self::ERROR_OK) {
             return false;
@@ -3089,19 +3187,19 @@
      *
      * @return string|bool On success APPENDUID response (if available) or True, False on failure
      */
-    public function appendFromFile($mailbox, $path, $headers=null, $flags = array(), $date = null, $binary = false)
+    public function appendFromFile($mailbox, $path, $headers = null, $flags = [], $date = null, $binary = false)
     {
         // open message file
         if (file_exists(realpath($path))) {
             $fp = fopen($path, 'r');
         }
 
-        if (!$fp) {
+        if (empty($fp)) {
             $this->setError(self::ERROR_UNKNOWN, "Couldn't open $path for reading");
             return false;
         }
 
-        $message = array();
+        $message = [];
         if ($headers) {
             $message[] = trim($headers, "\r\n") . "\r\n\r\n";
         }
@@ -3115,7 +3213,7 @@
      *
      * @param string $mailbox Mailbox name
      *
-     * @return array Quota information
+     * @return array|false Quota information, False on error
      */
     public function getQuota($mailbox = null)
     {
@@ -3128,48 +3226,50 @@
         // * QUOTA user/sample (STORAGE 654 9765)
         // a0001 OK Completed
 
-        list($code, $response) = $this->execute('GETQUOTAROOT', array($this->escape($mailbox)), 0, '/^\* QUOTA /i');
+        [$code, $response] = $this->execute('GETQUOTAROOT', [$this->escape($mailbox)], 0, '/^\* QUOTA /i');
 
-        $result   = false;
-        $min_free = PHP_INT_MAX;
-        $all      = array();
+        if ($code != self::ERROR_OK) {
+            return false;
+        }
 
-        if ($code == self::ERROR_OK) {
-            foreach (explode("\n", $response) as $line) {
-                list(, , $quota_root) = $this->tokenizeResponse($line, 3);
+        $min_free = \PHP_INT_MAX;
+        $result   = [];
+        $all      = [];
 
-                $quotas = $this->tokenizeResponse($line, 1);
+        foreach (explode("\n", $response) as $line) {
+            $tokens     = $this->tokenizeResponse($line, 3);
+            $quota_root = $tokens[2] ?? null;
+            $quotas     = $this->tokenizeResponse($line, 1);
 
-                if (empty($quotas)) {
-                    continue;
-                }
+            if (empty($quotas)) {
+                continue;
+            }
 
-                foreach (array_chunk($quotas, 3) as $quota) {
-                    list($type, $used, $total) = $quota;
-                    $type = strtolower($type);
+            foreach (array_chunk($quotas, 3) as $quota) {
+                [$type, $used, $total] = $quota;
+                $type = strtolower($type);
 
-                    if ($type && $total) {
-                        $all[$quota_root][$type]['used']  = intval($used);
-                        $all[$quota_root][$type]['total'] = intval($total);
-                    }
+                if ($type && $total) {
+                    $all[$quota_root][$type]['used']  = intval($used);
+                    $all[$quota_root][$type]['total'] = intval($total);
                 }
+            }
 
-                if (empty($all[$quota_root]['storage'])) {
-                    continue;
-                }
+            if (empty($all[$quota_root]['storage'])) {
+                continue;
+            }
 
-                $used  = $all[$quota_root]['storage']['used'];
-                $total = $all[$quota_root]['storage']['total'];
-                $free  = $total - $used;
-
-                // calculate lowest available space from all storage quotas
-                if ($free < $min_free) {
-                    $min_free          = $free;
-                    $result['used']    = $used;
-                    $result['total']   = $total;
-                    $result['percent'] = min(100, round(($used/max(1,$total))*100));
-                    $result['free']    = 100 - $result['percent'];
-                }
+            $used  = $all[$quota_root]['storage']['used'];
+            $total = $all[$quota_root]['storage']['total'];
+            $free  = $total - $used;
+
+            // calculate lowest available space from all storage quotas
+            if ($free < $min_free) {
+                $min_free          = $free;
+                $result['used']    = $used;
+                $result['total']   = $total;
+                $result['percent'] = min(100, round(($used / max(1, $total)) * 100));
+                $result['free']    = 100 - $result['percent'];
             }
         }
 
@@ -3186,11 +3286,11 @@
      * @param string $root  Quota root
      * @param array  $quota Quota limits e.g. ['storage' => 1024000']
      *
-     * @return boolean True on success, False on failure
+     * @return bool True on success, False on failure
      */
     public function setQuota($root, $quota)
     {
-        $fn = function ($key, $value) {
+        $fn = static function ($key, $value) {
             return strtoupper($key) . ' ' . $value;
         };
 
@@ -3199,7 +3299,7 @@
         $result = $this->execute('SETQUOTA', [$this->escape($root), "({$quota})"],
             self::COMMAND_NORESPONSE);
 
-        return ($result == self::ERROR_OK);
+        return $result == self::ERROR_OK;
     }
 
     /**
@@ -3209,7 +3309,7 @@
      * @param string $user    User name
      * @param mixed  $acl     ACL string or array
      *
-     * @return boolean True on success, False on failure
+     * @return bool True on success, False on failure
      *
      * @since 0.5-beta
      */
@@ -3219,11 +3319,12 @@
             $acl = implode('', $acl);
         }
 
-        $result = $this->execute('SETACL', array(
-            $this->escape($mailbox), $this->escape($user), strtolower($acl)),
-            self::COMMAND_NORESPONSE);
+        $result = $this->execute('SETACL',
+            [$this->escape($mailbox), $this->escape($user), strtolower($acl)],
+            self::COMMAND_NORESPONSE
+        );
 
-        return ($result == self::ERROR_OK);
+        return $result == self::ERROR_OK;
     }
 
     /**
@@ -3232,17 +3333,18 @@
      * @param string $mailbox Mailbox name
      * @param string $user    User name
      *
-     * @return boolean True on success, False on failure
+     * @return bool True on success, False on failure
      *
      * @since 0.5-beta
      */
     public function deleteACL($mailbox, $user)
     {
-        $result = $this->execute('DELETEACL', array(
-            $this->escape($mailbox), $this->escape($user)),
-            self::COMMAND_NORESPONSE);
+        $result = $this->execute('DELETEACL',
+            [$this->escape($mailbox), $this->escape($user)],
+            self::COMMAND_NORESPONSE
+        );
 
-        return ($result == self::ERROR_OK);
+        return $result == self::ERROR_OK;
     }
 
     /**
@@ -3251,11 +3353,12 @@
      * @param string $mailbox Mailbox name
      *
      * @return array User-rights array on success, NULL on error
+     *
      * @since 0.5-beta
      */
     public function getACL($mailbox)
     {
-        list($code, $response) = $this->execute('GETACL', array($this->escape($mailbox)), 0, '/^\* ACL /i');
+        [$code, $response] = $this->execute('GETACL', [$this->escape($mailbox)], 0, '/^\* ACL /i');
 
         if ($code == self::ERROR_OK && $response) {
             // Parse server response (remove "* ACL ")
@@ -3269,15 +3372,15 @@
             // so we could return only standard rights defined in RFC4314,
             // excluding 'c' and 'd' defined in RFC2086.
             if ($size % 2 == 0) {
-                for ($i=0; $i<$size; $i++) {
+                for ($i = 0; $i < $size; $i++) {
                     $ret[$ret[$i]] = str_split($ret[++$i]);
-                    unset($ret[$i-1]);
+                    unset($ret[$i - 1]);
                     unset($ret[$i]);
                 }
                 return $ret;
             }
 
-            $this->setError(self::ERROR_COMMAND, "Incomplete ACL response");
+            $this->setError(self::ERROR_COMMAND, 'Incomplete ACL response');
         }
     }
 
@@ -3288,12 +3391,13 @@
      * @param string $user    User name
      *
      * @return array List of user rights
+     *
      * @since 0.5-beta
      */
     public function listRights($mailbox, $user)
     {
-        list($code, $response) = $this->execute('LISTRIGHTS',
-            array($this->escape($mailbox), $this->escape($user)), 0, '/^\* LISTRIGHTS /i');
+        [$code, $response] = $this->execute('LISTRIGHTS',
+            [$this->escape($mailbox), $this->escape($user)], 0, '/^\* LISTRIGHTS /i');
 
         if ($code == self::ERROR_OK && $response) {
             // Parse server response (remove "* LISTRIGHTS ")
@@ -3304,10 +3408,10 @@
             $granted  = $this->tokenizeResponse($response, 1);
             $optional = trim($response);
 
-            return array(
+            return [
                 'granted'  => str_split($granted),
                 'optional' => explode(' ', $optional),
-            );
+            ];
         }
     }
 
@@ -3317,11 +3421,12 @@
      * @param string $mailbox Mailbox name
      *
      * @return array MYRIGHTS response on success, NULL on error
+     *
      * @since 0.5-beta
      */
     public function myRights($mailbox)
     {
-        list($code, $response) = $this->execute('MYRIGHTS', array($this->escape($mailbox)), 0, '/^\* MYRIGHTS /i');
+        [$code, $response] = $this->execute('MYRIGHTS', [$this->escape($mailbox)], 0, '/^\* MYRIGHTS /i');
 
         if ($code == self::ERROR_OK && $response) {
             // Parse server response (remove "* MYRIGHTS ")
@@ -3340,13 +3445,14 @@
      * @param string $mailbox Mailbox name
      * @param array  $entries Entry-value array (use NULL value as NIL)
      *
-     * @return boolean True on success, False on failure
+     * @return bool True on success, False on failure
+     *
      * @since 0.5-beta
      */
     public function setMetadata($mailbox, $entries)
     {
         if (!is_array($entries) || empty($entries)) {
-            $this->setError(self::ERROR_COMMAND, "Wrong argument for SETMETADATA command");
+            $this->setError(self::ERROR_COMMAND, 'Wrong argument for SETMETADATA command');
             return false;
         }
 
@@ -3355,11 +3461,12 @@
         }
 
         $entries = implode(' ', $entries);
-        $result = $this->execute('SETMETADATA', array(
-            $this->escape($mailbox), '(' . $entries . ')'),
-            self::COMMAND_NORESPONSE);
+        $result = $this->execute('SETMETADATA',
+            [$this->escape($mailbox), '(' . $entries . ')'],
+            self::COMMAND_NORESPONSE
+        );
 
-        return ($result == self::ERROR_OK);
+        return $result == self::ERROR_OK;
     }
 
     /**
@@ -3368,7 +3475,7 @@
      * @param string $mailbox Mailbox name
      * @param array  $entries Entry names array
      *
-     * @return boolean True on success, False on failure
+     * @return bool True on success, False on failure
      *
      * @since 0.5-beta
      */
@@ -3379,10 +3486,11 @@
         }
 
         if (empty($entries)) {
-            $this->setError(self::ERROR_COMMAND, "Wrong argument for SETMETADATA command");
+            $this->setError(self::ERROR_COMMAND, 'Wrong argument for SETMETADATA command');
             return false;
         }
 
+        $data = [];
         foreach ($entries as $entry) {
             $data[$entry] = null;
         }
@@ -3401,44 +3509,39 @@
      *
      * @since 0.5-beta
      */
-    public function getMetadata($mailbox, $entries, $options=array())
+    public function getMetadata($mailbox, $entries, $options = [])
     {
         if (!is_array($entries)) {
-            $entries = array($entries);
+            $entries = [$entries];
         }
 
-        // create entries string
-        foreach ($entries as $idx => $name) {
-            $entries[$idx] = $this->escape($name);
-        }
-
-        $optlist = '';
-        $entlist = '(' . implode(' ', $entries) . ')';
+        $args = [];
 
         // create options string
         if (is_array($options)) {
-            $options = array_change_key_case($options, CASE_UPPER);
-            $opts = array();
+            $options = array_change_key_case($options, \CASE_UPPER);
+            $opts    = [];
 
             if (!empty($options['MAXSIZE'])) {
-                $opts[] = 'MAXSIZE '.intval($options['MAXSIZE']);
+                $opts[] = 'MAXSIZE ' . intval($options['MAXSIZE']);
             }
-            if (!empty($options['DEPTH'])) {
-                $opts[] = 'DEPTH '.intval($options['DEPTH']);
+
+            if (isset($options['DEPTH'])) {
+                $opts[] = 'DEPTH ' . $this->escape($options['DEPTH']);
             }
 
-            if ($opts) {
-                $optlist = '(' . implode(' ', $opts) . ')';
+            if (!empty($opts)) {
+                $args[] = $opts;
             }
         }
 
-        $optlist .= ($optlist ? ' ' : '') . $entlist;
+        $args[] = $this->escape($mailbox);
+        $args[] = array_map([$this, 'escape'], $entries);
 
-        list($code, $response) = $this->execute('GETMETADATA', array(
-            $this->escape($mailbox), $optlist));
+        [$code, $response] = $this->execute('GETMETADATA', $args);
 
         if ($code == self::ERROR_OK) {
-            $result = array();
+            $result = [];
             $data   = $this->tokenizeResponse($response);
 
             // The METADATA response can contain multiple entries in a single
@@ -3450,8 +3553,8 @@
                     && is_array($data[++$i])
                 ) {
                     for ($x = 0, $size2 = count($data[$i]); $x < $size2; $x += 2) {
-                        if ($data[$i][$x+1] !== null) {
-                            $result[$mbox][$data[$i][$x]] = $data[$i][$x+1];
+                        if ($data[$i][$x + 1] !== null) {
+                            $result[$mbox][$data[$i][$x]] = $data[$i][$x + 1];
                         }
                     }
                 }
@@ -3468,13 +3571,14 @@
      * @param array  $data    Data array where each item is an array with
      *                        three elements: entry name, attribute name, value
      *
-     * @return boolean True on success, False on failure
+     * @return bool True on success, False on failure
+     *
      * @since 0.5-beta
      */
     public function setAnnotation($mailbox, $data)
     {
         if (!is_array($data) || empty($data)) {
-            $this->setError(self::ERROR_COMMAND, "Wrong argument for SETANNOTATION command");
+            $this->setError(self::ERROR_COMMAND, 'Wrong argument for SETANNOTATION command');
             return false;
         }
 
@@ -3485,10 +3589,9 @@
         }
 
         $entries = implode(' ', $entries);
-        $result  = $this->execute('SETANNOTATION', array(
-            $this->escape($mailbox), $entries), self::COMMAND_NORESPONSE);
+        $result  = $this->execute('SETANNOTATION', [$this->escape($mailbox), $entries], self::COMMAND_NORESPONSE);
 
-        return ($result == self::ERROR_OK);
+        return $result == self::ERROR_OK;
     }
 
     /**
@@ -3498,14 +3601,14 @@
      * @param array  $data    Data array where each item is an array with
      *                        two elements: entry name and attribute name
      *
-     * @return boolean True on success, False on failure
+     * @return bool True on success, False on failure
      *
      * @since 0.5-beta
      */
     public function deleteAnnotation($mailbox, $data)
     {
         if (!is_array($data) || empty($data)) {
-            $this->setError(self::ERROR_COMMAND, "Wrong argument for SETANNOTATION command");
+            $this->setError(self::ERROR_COMMAND, 'Wrong argument for SETANNOTATION command');
             return false;
         }
 
@@ -3526,7 +3629,7 @@
     public function getAnnotation($mailbox, $entries, $attribs)
     {
         if (!is_array($entries)) {
-            $entries = array($entries);
+            $entries = [$entries];
         }
 
         // create entries string
@@ -3537,7 +3640,7 @@
         $entries = '(' . implode(' ', $entries) . ')';
 
         if (!is_array($attribs)) {
-            $attribs = array($attribs);
+            $attribs = [$attribs];
         }
 
         // create attributes string
@@ -3546,24 +3649,23 @@
         }
         $attribs = '(' . implode(' ', $attribs) . ')';
 
-        list($code, $response) = $this->execute('GETANNOTATION', array(
-            $this->escape($mailbox), $entries, $attribs));
+        [$code, $response] = $this->execute('GETANNOTATION', [$this->escape($mailbox), $entries, $attribs]);
 
         if ($code == self::ERROR_OK) {
-            $result = array();
-            $data   = $this->tokenizeResponse($response);
+            $result     = [];
+            $data       = $this->tokenizeResponse($response);
+            $last_entry = null;
 
             // Here we returns only data compatible with METADATA result format
             if (!empty($data) && ($size = count($data))) {
-                for ($i=0; $i<$size; $i++) {
+                for ($i = 0; $i < $size; $i++) {
                     $entry = $data[$i];
                     if (isset($mbox) && is_array($entry)) {
                         $attribs = $entry;
                         $entry   = $last_entry;
-                    }
-                    else if ($entry == '*') {
-                        if ($data[$i+1] == 'ANNOTATION') {
-                            $mbox = $data[$i+2];
+                    } elseif ($entry == '*') {
+                        if ($data[$i + 1] == 'ANNOTATION') {
+                            $mbox = $data[$i + 2];
                             unset($data[$i]);   // "*"
                             unset($data[++$i]); // "ANNOTATION"
                             unset($data[++$i]); // Mailbox
@@ -3574,27 +3676,25 @@
                             unset($data[$i]);
                         }
                         continue;
-                    }
-                    else if (isset($mbox)) {
+                    } elseif (isset($mbox)) {
                         $attribs = $data[++$i];
-                    }
-                    else {
+                    } else {
                         unset($data[$i]);
                         continue;
                     }
 
                     if (!empty($attribs)) {
-                        for ($x=0, $len=count($attribs); $x<$len;) {
+                        for ($x = 0, $len = count($attribs); $x < $len;) {
                             $attr  = $attribs[$x++];
                             $value = $attribs[$x++];
                             if ($attr == 'value.priv' && $value !== null) {
                                 $result[$mbox]['/private' . $entry] = $value;
-                            }
-                            else if ($attr == 'value.shared' && $value !== null) {
+                            } elseif ($attr == 'value.shared' && $value !== null) {
                                 $result[$mbox]['/shared' . $entry] = $value;
                             }
                         }
                     }
+
                     $last_entry = $entry;
                     unset($data[$i]);
                 }
@@ -3611,15 +3711,16 @@
      * @param int    $id      Message sequence number or UID
      * @param bool   $is_uid  True if $id is an UID
      *
-     * @return array/bool Body structure array or False on error.
+     * @return array|bool Body structure array or False on error.
+     *
      * @since 0.6
      */
     public function getStructure($mailbox, $id, $is_uid = false)
     {
-        $result = $this->fetch($mailbox, $id, $is_uid, array('BODYSTRUCTURE'));
+        $result = $this->fetch($mailbox, $id, $is_uid, ['BODYSTRUCTURE']);
 
-        if (is_array($result)) {
-            $result = array_shift($result);
+        if (is_array($result) && !empty($result)) {
+            $result = array_first($result);
             return $result->bodystructure;
         }
 
@@ -3637,7 +3738,7 @@
     public static function getStructurePartData($structure, $part)
     {
         $part_a = self::getStructurePartArray($structure, $part);
-        $data   = array();
+        $data   = [];
 
         if (empty($part_a)) {
             return $data;
@@ -3646,17 +3747,16 @@
         // content-type
         if (is_array($part_a[0])) {
             $data['type'] = 'multipart';
-        }
-        else {
+        } else {
             $data['type']     = strtolower($part_a[0]);
             $data['subtype']  = strtolower($part_a[1]);
             $data['encoding'] = strtolower($part_a[5]);
 
             // charset
             if (is_array($part_a[2])) {
-               foreach ($part_a[2] as $key => $val) {
+                foreach ($part_a[2] as $key => $val) {
                     if (strcasecmp($val, 'charset') == 0) {
-                        $data['charset'] = $part_a[2][$key+1];
+                        $data['charset'] = $part_a[2][$key + 1];
                         break;
                     }
                 }
@@ -3688,13 +3788,12 @@
         if (strpos($part, '.') > 0) {
             $orig_part = $part;
             $pos       = strpos($part, '.');
-            $rest      = substr($orig_part, $pos+1);
+            $rest      = substr($orig_part, $pos + 1);
             $part      = substr($orig_part, 0, $pos);
 
-            return self::getStructurePartArray($a[$part-1], $rest);
-        }
-        else if ($part > 0) {
-            return (is_array($a[$part-1])) ? $a[$part-1] : $a;
+            return self::getStructurePartArray($a[$part - 1], $rest);
+        } elseif ($part > 0) {
+            return is_array($a[$part - 1]) ? $a[$part - 1] : $a;
         }
     }
 
@@ -3702,6 +3801,7 @@
      * Creates next command identifier (tag)
      *
      * @return string Command identifier
+     *
      * @since 0.5-beta
      */
     public function nextTag()
@@ -3721,9 +3821,10 @@
      * @param string $filter    Line filter (regexp)
      *
      * @return mixed Response code or list of response code and data
+     *
      * @since 0.5-beta
      */
-    public function execute($command, $arguments = array(), $options = 0, $filter = null)
+    public function execute($command, $arguments = [], $options = 0, $filter = null)
     {
         $tag      = $this->nextTag();
         $query    = $tag . ' ' . $command;
@@ -3737,20 +3838,19 @@
         }
 
         // Send command
-        if (!$this->putLineC($query, true, ($options & self::COMMAND_ANONYMIZED))) {
+        if (!$this->putLineC($query, true, $options & self::COMMAND_ANONYMIZED)) {
             preg_match('/^[A-Z0-9]+ ((UID )?[A-Z]+)/', $query, $matches);
             $cmd = $matches[1] ?: 'UNKNOWN';
             $this->setError(self::ERROR_COMMAND, "Failed to send $cmd command");
 
-            return $noresp ? self::ERROR_COMMAND : array(self::ERROR_COMMAND, '');
+            return $noresp ? self::ERROR_COMMAND : [self::ERROR_COMMAND, ''];
         }
 
         // Parse response
         do {
-            $line = $this->readLine(4096);
+            $line = $this->readFullLine(4096);
 
             if ($response !== null) {
-                // TODO: Better string literals handling with filter
                 if (!$filter || preg_match($filter, $line)) {
                     $response .= $line;
                 }
@@ -3758,12 +3858,11 @@
 
             // parse untagged response for [COPYUID 1204196876 3456:3457 123:124] (RFC6851)
             if ($line && $command == 'UID MOVE') {
-                if (preg_match("/^\* OK \[COPYUID [0-9]+ ([0-9,:]+) ([0-9,:]+)\]/i", $line, $m)) {
-                    $this->data['COPYUID'] = array($m[1], $m[2]);
+                if (preg_match('/^\\* OK \\[COPYUID [0-9]+ ([0-9,:]+) ([0-9,:]+)\\]/i', $line, $m)) {
+                    $this->data['COPYUID'] = [$m[1], $m[2]];
                 }
             }
-        }
-        while (!$this->startsWith($line, $tag . ' ', true, true));
+        } while (!$this->startsWith($line, $tag . ' ', true, true));
 
         $code = $this->parseResult($line, $command . ': ');
 
@@ -3786,10 +3885,10 @@
 
         // return last line only (without command tag, result and response code)
         if ($line && ($options & self::COMMAND_LASTLINE)) {
-            $response = preg_replace("/^$tag (OK|NO|BAD|BYE|PREAUTH)?\s*(\[[a-z-]+\])?\s*/i", '', trim($line));
+            $response = preg_replace("/^$tag (OK|NO|BAD|BYE|PREAUTH)?\\s*(\\[[a-z-]+\\])?\\s*/i", '', trim($line));
         }
 
-        return $noresp ? $code : array($code, $response);
+        return $noresp ? $code : [$code, $response];
     }
 
     /**
@@ -3799,11 +3898,12 @@
      * @param int    $num  Number of tokens to return
      *
      * @return mixed Tokens array or string if $num=1
+     *
      * @since 0.5-beta
      */
-    public static function tokenizeResponse(&$str, $num=0)
+    public static function tokenizeResponse(&$str, $num = 0)
     {
-        $result = array();
+        $result = [];
 
         while (!$num || count($result) < $num) {
             // remove spaces from the beginning of the string
@@ -3816,62 +3916,63 @@
 
             switch ($str[0]) {
 
-            // String literal
-            case '{':
-                if (($epos = strpos($str, "}\r\n", 1)) == false) {
-                    // error
-                }
-                if (!is_numeric(($bytes = substr($str, 1, $epos - 1)))) {
-                    // error
-                }
+                // String literal
+                case '{':
+                    if (($epos = strpos($str, "}\r\n", 1)) == false) {
+                        // error
+                    }
+                    if (!is_numeric($bytes = substr($str, 1, $epos - 1))) {
+                        // error
+                    }
 
-                $result[] = $bytes ? substr($str, $epos + 3, $bytes) : '';
-                $str      = substr($str, $epos + 3 + $bytes);
-                break;
+                    $result[] = $bytes ? substr($str, $epos + 3, $bytes) : '';
+                    $str      = substr($str, $epos + 3 + $bytes);
+                    break;
 
-            // Quoted string
-            case '"':
-                $len = strlen($str);
+                    // Quoted string (<< reindent once https://github.com/PHP-CS-Fixer/PHP-CS-Fixer/issues/7179 is fixed)
+                case '"':
+                    $len = strlen($str);
 
-                for ($pos=1; $pos<$len; $pos++) {
-                    if ($str[$pos] == '"') {
-                        break;
-                    }
-                    if ($str[$pos] == "\\") {
-                        if ($str[$pos + 1] == '"' || $str[$pos + 1] == "\\") {
-                            $pos++;
+                    for ($pos = 1; $pos < $len; $pos++) {
+                        if ($str[$pos] == '"') {
+                            break;
+                        }
+                        if ($str[$pos] == '\\') {
+                            if ($str[$pos + 1] == '"' || $str[$pos + 1] == '\\') {
+                                $pos++;
+                            }
                         }
                     }
-                }
 
-                // we need to strip slashes for a quoted string
-                $result[] = stripslashes(substr($str, 1, $pos - 1));
-                $str      = substr($str, $pos + 1);
-                break;
+                    // we need to strip slashes for a quoted string
+                    $result[] = stripslashes(substr($str, 1, $pos - 1));
+                    $str      = substr($str, $pos + 1);
+                    break;
 
-            // Parenthesized list
-            case '(':
-                $str      = substr($str, 1);
-                $result[] = self::tokenizeResponse($str);
-                break;
+                    // Parenthesized list (<< reindent once https://github.com/PHP-CS-Fixer/PHP-CS-Fixer/issues/7179 is fixed)
+                case '(':
+                    $str      = substr($str, 1);
+                    $result[] = self::tokenizeResponse($str);
+                    break;
 
-            case ')':
-                $str = substr($str, 1);
-                return $result;
+                case ')':
+                    $str = substr($str, 1);
+                    return $result;
 
-            // String atom, number, astring, NIL, *, %
-            default:
-                // excluded chars: SP, CTL, ), DEL
-                // we do not exclude [ and ] (#1489223)
-                if (preg_match('/^([^\x00-\x20\x29\x7F]+)/', $str, $m)) {
-                    $result[] = $m[1] == 'NIL' ? null : $m[1];
-                    $str      = substr($str, strlen($m[1]));
-                }
-                break;
+                    // String atom, number, astring, NIL, *, % (<< reindent once https://github.com/PHP-CS-Fixer/PHP-CS-Fixer/issues/7179 is fixed)
+                default:
+                    // excluded chars: SP, CTL, ), DEL
+                    // we do not exclude [ and ] (#1489223)
+                    if (preg_match('/^([^\x00-\x20\x29\x7F]+)/', $str, $m)) {
+                        $result[] = $m[1] == 'NIL' ? null : $m[1];
+                        $str      = substr($str, strlen($m[1]));
+                    }
+
+                    break;
             }
         }
 
-        return $num == 1 ? $result[0] : $result;
+        return $num == 1 ? ($result[0] ?? '') : $result;
     }
 
     /**
@@ -3879,16 +3980,16 @@
      */
     protected static function r_implode($element)
     {
+        if (!is_array($element)) {
+            return $element;
+        }
+
+        reset($element);
+
         $string = '';
 
-        if (is_array($element)) {
-            reset($element);
-            foreach ($element as $value) {
-                $string .= ' ' . self::r_implode($value);
-            }
-        }
-        else {
-            return $element;
+        foreach ($element as $value) {
+            $string .= ' ' . self::r_implode($value);
         }
 
         return '(' . trim($string) . ')';
@@ -3902,7 +4003,7 @@
      *
      * @return string Compressed sequence-set
      */
-    public static function compressMessageSet($messages, $force=false)
+    public static function compressMessageSet($messages, $force = false)
     {
         // given a comma delimited list of independent mid's,
         // compresses by grouping sequences together
@@ -3923,7 +4024,7 @@
 
         sort($messages);
 
-        $result = array();
+        $result = [];
         $start  = $prev = $messages[0];
 
         foreach ($messages as $id) {
@@ -3931,8 +4032,7 @@
             if ($incr > 1) { // found a gap
                 if ($start == $prev) {
                     $result[] = $prev; // push single id
-                }
-                else {
+                } else {
                     $result[] = $start . ':' . $prev; // push sequence as start_id:end_id
                 }
                 $start = $id; // start of new sequence
@@ -3943,9 +4043,8 @@
         // handle the last sequence/id
         if ($start == $prev) {
             $result[] = $prev;
-        }
-        else {
-            $result[] = $start.':'.$prev;
+        } else {
+            $result[] = $start . ':' . $prev;
         }
 
         // return as comma separated string
@@ -3964,19 +4063,25 @@
     public static function uncompressMessageSet($messages)
     {
         if (empty($messages)) {
-            return array();
+            return [];
         }
 
-        $result   = array();
+        $result   = [];
         $messages = explode(',', $messages);
 
         foreach ($messages as $idx => $part) {
             $items = explode(':', $part);
-            $max   = max($items[0], $items[1]);
 
-            for ($x=$items[0]; $x<=$max; $x++) {
-                $result[] = (int)$x;
+            if (!empty($items[1]) && $items[1] > $items[0]) {
+                $max = $items[1];
+            } else {
+                $max = $items[0];
+            }
+
+            for ($x = $items[0]; $x <= $max; $x++) {
+                $result[] = (int) $x;
             }
+
             unset($messages[$idx]);
         }
 
@@ -3990,7 +4095,7 @@
     {
         unset($this->data['STATUS:' . $mailbox]);
 
-        $keys = array('EXISTS', 'RECENT', 'UNSEEN', 'UID-MAP');
+        $keys = ['EXISTS', 'RECENT', 'UNSEEN', 'UID-MAP'];
 
         foreach ($keys as $key) {
             unset($this->data[$key]);
@@ -4004,8 +4109,8 @@
     {
         $this->clear_status_cache($this->selected);
 
-        $keys = array('UIDNEXT', 'UIDVALIDITY', 'HIGHESTMODSEQ', 'NOMODSEQ',
-            'PERMANENTFLAGS', 'QRESYNC', 'VANISHED', 'READ-WRITE');
+        $keys = ['UIDNEXT', 'UIDVALIDITY', 'HIGHESTMODSEQ', 'NOMODSEQ',
+            'PERMANENTFLAGS', 'QRESYNC', 'VANISHED', 'READ-WRITE'];
 
         foreach ($keys as $key) {
             unset($this->data[$key]);
@@ -4021,19 +4126,19 @@
      */
     protected function flagsToStr($flags)
     {
-        foreach ((array)$flags as $idx => $flag) {
+        foreach ((array) $flags as $idx => $flag) {
             if ($flag = $this->flags[strtoupper($flag)]) {
                 $flags[$idx] = $flag;
             }
         }
 
-        return implode(' ', (array)$flags);
+        return implode(' ', (array) $flags);
     }
 
     /**
      * CAPABILITY response parser
      */
-    protected function parseCapability($str, $trusted=false)
+    protected function parseCapability($str, $trusted = false)
     {
         $str = preg_replace('/^\* CAPABILITY /i', '', $str);
 
@@ -4045,23 +4150,26 @@
 
         if (!isset($this->prefs['literal+']) && in_array('LITERAL+', $this->capability)) {
             $this->prefs['literal+'] = true;
+        } elseif (!isset($this->prefs['literal-']) && in_array('LITERAL-', $this->capability)) {
+            $this->prefs['literal-'] = true;
         }
 
         if ($trusted) {
-            $this->capability_readed = true;
+            $this->capability_read = true;
         }
     }
 
     /**
      * Escapes a string when it contains special characters (RFC3501)
      *
-     * @param string  $string       IMAP string
-     * @param boolean $force_quotes Forces string quoting (for atoms)
+     * @param string $string       IMAP string
+     * @param bool   $force_quotes Forces string quoting (for atoms)
      *
      * @return string String atom, quoted-string or string literal
+     *
      * @todo lists
      */
-    public static function escape($string, $force_quotes=false)
+    public static function escape($string, $force_quotes = false)
     {
         if ($string === null) {
             return 'NIL';
@@ -4088,8 +4196,8 @@
     /**
      * Set the value of the debugging flag.
      *
-     * @param bool      $debug   New value for the debugging flag.
-     * @param ?callable $handler Logging handler function
+     * @param bool     $debug   New value for the debugging flag.
+     * @param callable $handler Logging handler function
      *
      * @since 0.5-stable
      */
@@ -4119,9 +4227,8 @@
         }
 
         if ($this->debug_handler) {
-            call_user_func_array($this->debug_handler, array($this, $message));
-        }
-        else {
+            call_user_func_array($this->debug_handler, [$this, $message]);
+        } else {
             echo "DEBUG: $message\n";
         }
     }
diff --git a/src/tests/Infrastructure/IMAPTest.php b/src/tests/Infrastructure/IMAPTest.php
--- a/src/tests/Infrastructure/IMAPTest.php
+++ b/src/tests/Infrastructure/IMAPTest.php
@@ -49,7 +49,6 @@
         $email = self::$user->email;
         $mailbox = "user/{$email}/test";
 
-        // $this->assertTrue($imap->createFolder($mailbox));
         $imap->createFolder($mailbox);
         $this->assertEquals(1, count($imap->listMailboxes('', $mailbox)));
         $imap->setACL($mailbox, 'cyrus-admin', 'c');
@@ -58,13 +57,11 @@
             '/private/vendor/kolab/folder-type' => 'event'
         ]));
 
-
         $metadata = $imap->getMetadata($mailbox, [
             '/shared/vendor/kolab/folder-type',
             '/private/vendor/kolab/folder-type'
         ]);
 
-        print_r($metadata);
         $this->assertEquals('event', $metadata[$mailbox]['/shared/vendor/kolab/folder-type']);
         $this->assertEquals('event', $metadata[$mailbox]['/private/vendor/kolab/folder-type']);
 
@@ -72,6 +69,26 @@
         $this->assertEquals(0, count($imap->listMailboxes('', $mailbox)));
     }
 
+    /**
+     * Test for a Cyrus proxy bug regarding VANISHED modifier
+     * that is required by Kolab cache in webmail libkolab plugin
+     */
+    public function testFetchVanished()
+    {
+        $imap = $this->getImap();
+
+        $imap->createFolder('Test');
+
+        $this->assertTrue($imap->select('Test'));
+        $this->assertSame(['CONDSTORE', 'QRESYNC'], $imap->enable('QRESYNC'));
+
+        $result = $imap->fetch('Test', '1:*', true, ['FLAGS'], $imap->data['HIGHESTMODSEQ'], true);
+
+        // TODO: We check the command failure only, we would have to put some
+        // messages in the folder to test the command response is correct
+        $this->assertSame([], $result);
+    }
+
     /**
      * @doesNotPerformAssertions
      */
diff --git a/src/tests/TestCaseTrait.php b/src/tests/TestCaseTrait.php
--- a/src/tests/TestCaseTrait.php
+++ b/src/tests/TestCaseTrait.php
@@ -575,6 +575,7 @@
         if (!$createInBackends) {
             Queue::fake();
         }
+
         $user = User::firstOrCreate(['email' => $email], $attrib);
 
         if ($user->trashed()) {