diff --git a/lib/Autodiscover.php b/lib/Autodiscover.php
--- a/lib/Autodiscover.php
+++ b/lib/Autodiscover.php
@@ -156,17 +156,17 @@
             if ($value = $this->conf->get('autodiscover', $type)) {
                 $params = explode(';', $value);
 
-                $pass_secure = in_array($params[1], array('CRAM-MD5', 'DIGEST-MD5'));
+                $pass_secure = in_array($params[1] ?? null, array('CRAM-MD5', 'DIGEST-MD5'));
 
-                $host = $params[0];
+                $host = $params[0] ?? null;
                 $host = str_replace('%d', $this->config['domain'], $host);
                 $url  = parse_url($host);
 
                 $this->config[$type] = array(
                     'hostname'        => $url['host'],
                     'port'            => $url['port'],
-                    'socketType'      => $proto_map[$url['scheme']] ?: 'plain',
-                    'username'        => $this->config['login'] ?: $this->config['email'],
+                    'socketType'      => $proto_map[$url['scheme']] ?? 'plain',
+                    'username'        => $this->config['login'] ?? $this->config['email'],
                     'authentication'  => 'password-' . ($pass_secure ? 'encrypted' : 'cleartext'),
                 );
             }
diff --git a/lib/AutodiscoverMicrosoft.php b/lib/AutodiscoverMicrosoft.php
--- a/lib/AutodiscoverMicrosoft.php
+++ b/lib/AutodiscoverMicrosoft.php
@@ -159,11 +159,11 @@
 
         $dispname = $xml->createElement('DisplayName');
         $dispname = $user->appendChild($dispname);
-        $dispname->appendChild($xml->createTextNode($this->config['username']));
+        $dispname->appendChild($xml->createTextNode($this->config['username'] ?? null));
 
         $email = $xml->createElement('EMailAddress');
         $email = $user->appendChild($email);
-        $email->appendChild($xml->createTextNode($this->config['login'] ?: $this->config['email']));
+        $email->appendChild($xml->createTextNode($this->config['login'] ?? $this->config['email']));
 
         $element = $xml->createElement('Type');
         $element = $server->appendChild($element);
@@ -212,11 +212,11 @@
 
         $dispname = $xml->createElement('DisplayName');
         $dispname = $user->appendChild($dispname);
-        $dispname->appendChild($xml->createTextNode($this->config['username']));
+        $dispname->appendChild($xml->createTextNode($this->config['username'] ?? null));
 
         $email = $xml->createElement('AutoDiscoverSMTPAddress');
         $email = $user->appendChild($email);
-        $email->appendChild($xml->createTextNode($this->config['login'] ?: $this->config['email']));
+        $email->appendChild($xml->createTextNode($this->config['login'] ?? $this->config['email']));
 
         // @TODO: Microsoft supports also DAV protocol here
         foreach (array('imap', 'pop3', 'smtp') as $type) {
diff --git a/lib/Conf.php b/lib/Conf.php
--- a/lib/Conf.php
+++ b/lib/Conf.php
@@ -139,16 +139,18 @@
 
         // Fall back to whatever is the equivalent of auth_mechanism as the
         // section (i.e. 'ldap', or 'sql')
-        $auth_mech = $this->_conf['kolab']['auth_mechanism'];
-        if (isset($this->_conf[$auth_mech])) {
-            if (isset($this->_conf[$auth_mech][$key1])) {
-                return $this->_conf[$auth_mech][$key1];
+        if (isset($this->_conf['kolab'])) {
+            $auth_mech = $this->_conf['kolab']['auth_mechanism'] ?? null;
+            if ($auth_mech && isset($this->_conf[$auth_mech])) {
+                if (isset($this->_conf[$auth_mech][$key1])) {
+                    return $this->_conf[$auth_mech][$key1];
+                }
             }
-        }
 
-        // Fall back to global settings in the 'kolab' section.
-        if (isset($this->_conf['kolab'][$key1])) {
-            return $this->_conf['kolab'][$key1];
+            // Fall back to global settings in the 'kolab' section.
+            if (isset($this->_conf['kolab'][$key1])) {
+                return $this->_conf['kolab'][$key1];
+            }
         }
 
         return null;