diff --git a/src/app/Backends/IMAP.php b/src/app/Backends/IMAP.php
index ea41bf10..db4a1584 100644
--- a/src/app/Backends/IMAP.php
+++ b/src/app/Backends/IMAP.php
@@ -1,704 +1,712 @@
 <?php
 
 namespace App\Backends;
 
 use App\Group;
 use App\Resource;
 use App\SharedFolder;
 use App\User;
 
 class IMAP
 {
     /** @const array Group settings used by the backend */
     public const GROUP_SETTINGS = [];
 
     /** @const array Resource settings used by the backend */
     public const RESOURCE_SETTINGS = [
         'folder',
         'invitation_policy',
     ];
 
     /** @const array Shared folder settings used by the backend */
     public const SHARED_FOLDER_SETTINGS = [
         'folder',
         'acl',
     ];
 
     /** @const array User settings used by the backend */
     public const USER_SETTINGS = [];
 
 
     /** @const array Maps Kolab permissions to IMAP permissions */
     private const ACL_MAP = [
         'read-only' => 'lrs',
         'read-write' => 'lrswitedn',
         'full' => 'lrswipkxtecdn',
     ];
 
     /**
      * Delete a group.
      *
      * @param \App\Group $group Group
      *
      * @return bool True if a group was deleted successfully, False otherwise
      * @throws \Exception
      */
     public static function deleteGroup(Group $group): bool
     {
         $domainName = explode('@', $group->email, 2)[1];
 
         // Cleanup ACL
         // FIXME: Since all groups in Kolab4 have email address,
         //        should we consider using it in ACL instead of the name?
         //        Also we need to decide what to do and configure IMAP appropriately,
         //        right now groups in ACL does not work for me at all.
         \App\Jobs\IMAP\AclCleanupJob::dispatch($group->name, $domainName);
 
         return true;
     }
 
     /**
      * Create a mailbox.
      *
      * @param \App\User $user User
      *
      * @return bool True if a mailbox was created successfully, False otherwise
      * @throws \Exception
      */
     public static function createUser(User $user): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         $mailbox = self::toUTF7('user/' . $user->email);
 
         // Mailbox already exists
         if (self::folderExists($imap, $mailbox)) {
             $imap->closeConnection();
             self::createDefaultFolders($user);
             return true;
         }
 
         // Create the mailbox
         if (!$imap->createFolder($mailbox)) {
             \Log::error("Failed to create mailbox {$mailbox}");
             $imap->closeConnection();
             return false;
         }
 
         // Wait until it's propagated (for Cyrus Murder setup)
         // FIXME: Do we still need this?
         if (strpos($imap->conn->data['GREETING'] ?? '', 'Cyrus IMAP Murder') !== false) {
             $tries = 30;
             while ($tries-- > 0) {
                 $folders = $imap->listMailboxes('', $mailbox);
                 if (is_array($folders) && count($folders)) {
                     break;
                 }
                 sleep(1);
                 $imap->closeConnection();
                 $imap = self::initIMAP($config);
             }
         }
 
         // Set quota
         $quota = $user->countEntitlementsBySku('storage') * 1048576;
         if ($quota) {
             $imap->setQuota($mailbox, ['storage' => $quota]);
         }
 
         self::createDefaultFolders($user);
 
         $imap->closeConnection();
 
         return true;
     }
 
     /**
      * Create default folders for the user.
      *
      * @param \App\User $user User
      */
     public static function createDefaultFolders(User $user): void
     {
         if ($defaultFolders = \config('imap.default_folders')) {
             $config = self::getConfig();
             // Log in as user to set private annotations and subscription state
             $imap = self::initIMAP($config, $user->email);
             foreach ($defaultFolders as $name => $folderconfig) {
                 try {
                     $mailbox = self::toUTF7($name);
                     self::createFolder($imap, $mailbox, true, $folderconfig['metadata']);
                 } catch (\Exception $e) {
                     \Log::warning("Failed to create the default folder" . $e->getMessage());
                 }
             }
             $imap->closeConnection();
         }
     }
 
     /**
      * Delete a mailbox.
      *
      * @param \App\User $user User
      *
      * @return bool True if a mailbox was deleted successfully, False otherwise
      * @throws \Exception
      */
     public static function deleteUser(User $user): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         $mailbox = self::toUTF7('user/' . $user->email);
 
         // To delete the mailbox cyrus-admin needs extra permissions
         $imap->setACL($mailbox, $config['user'], 'c');
 
         // Delete the mailbox (no need to delete subfolders?)
         $result = $imap->deleteFolder($mailbox);
 
+        if (!$result) {
+            // Ignore the error if the folder doesn't exist (maybe it was removed already).
+            if (!self::folderExists($imap, $mailbox)) {
+                \Log::info("The mailbox to delete was already removed: $mailbox");
+                $result = true;
+            }
+        }
+
         $imap->closeConnection();
 
         // Cleanup ACL
         \App\Jobs\IMAP\AclCleanupJob::dispatch($user->email);
 
         return $result;
     }
 
     /**
      * Update a mailbox (quota).
      *
      * @param \App\User $user User
      *
      * @return bool True if a mailbox was updated successfully, False otherwise
      * @throws \Exception
      */
     public static function updateUser(User $user): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         $mailbox = self::toUTF7('user/' . $user->email);
         $result = true;
 
         // Set quota
         $quota = $user->countEntitlementsBySku('storage') * 1048576;
         if ($quota) {
             $result = $imap->setQuota($mailbox, ['storage' => $quota]);
         }
 
         $imap->closeConnection();
 
         return $result;
     }
 
     /**
      * Create a resource.
      *
      * @param \App\Resource $resource Resource
      *
      * @return bool True if a resource was created successfully, False otherwise
      * @throws \Exception
      */
     public static function createResource(Resource $resource): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         $settings = $resource->getSettings(['invitation_policy', 'folder']);
         $mailbox = self::toUTF7($settings['folder']);
 
         $acl = null;
         if (!empty($settings['invitation_policy'])) {
             if (preg_match('/^manual:(\S+@\S+)$/', $settings['invitation_policy'], $m)) {
                 $acl = ["{$m[1]}, full"];
             }
         }
         self::createFolder($imap, $mailbox, false, ['/shared/vendor/kolab/folder-type' => 'event'], $acl);
 
         $imap->closeConnection();
 
         return true;
     }
 
     /**
      * Update a resource.
      *
      * @param \App\Resource $resource Resource
      * @param array         $props    Old resource properties
      *
      * @return bool True if a resource was updated successfully, False otherwise
      * @throws \Exception
      */
     public static function updateResource(Resource $resource, array $props = []): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         $settings = $resource->getSettings(['invitation_policy', 'folder']);
         $folder = $settings['folder'];
         $mailbox = self::toUTF7($folder);
 
         // Rename the mailbox (only possible if we have the old folder)
         if (!empty($props['folder']) && $props['folder'] != $folder) {
             $oldMailbox = self::toUTF7($props['folder']);
 
             if (!$imap->renameFolder($oldMailbox, $mailbox)) {
                 \Log::error("Failed to rename mailbox {$oldMailbox} to {$mailbox}");
                 $imap->closeConnection();
                 return false;
             }
         }
 
         // ACL
         $acl = [];
         if (!empty($settings['invitation_policy'])) {
             if (preg_match('/^manual:(\S+@\S+)$/', $settings['invitation_policy'], $m)) {
                 $acl = ["{$m[1]}, full"];
             }
         }
         self::aclUpdate($imap, $mailbox, $acl);
 
         $imap->closeConnection();
 
         return true;
     }
 
     /**
      * Delete a resource.
      *
      * @param \App\Resource $resource Resource
      *
      * @return bool True if a resource was deleted successfully, False otherwise
      * @throws \Exception
      */
     public static function deleteResource(Resource $resource): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         $settings = $resource->getSettings(['folder']);
         $mailbox = self::toUTF7($settings['folder']);
 
         // To delete the mailbox cyrus-admin needs extra permissions
         $imap->setACL($mailbox, $config['user'], 'c');
 
         // Delete the mailbox (no need to delete subfolders?)
         $result = $imap->deleteFolder($mailbox);
 
         $imap->closeConnection();
 
         return $result;
     }
 
     /**
      * Create a shared folder.
      *
      * @param \App\SharedFolder $folder Shared folder
      *
      * @return bool True if a falder was created successfully, False otherwise
      * @throws \Exception
      */
     public static function createSharedFolder(SharedFolder $folder): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         $settings = $folder->getSettings(['acl', 'folder']);
         $acl = !empty($settings['acl']) ? json_decode($settings['acl'], true) : null;
         $mailbox = self::toUTF7($settings['folder']);
 
         self::createFolder($imap, $mailbox, false, ['/shared/vendor/kolab/folder-type' => $folder->type], $acl);
 
         $imap->closeConnection();
 
         return true;
     }
 
     /**
      * Update a shared folder.
      *
      * @param \App\SharedFolder $folder Shared folder
      * @param array             $props  Old folder properties
      *
      * @return bool True if a falder was updated successfully, False otherwise
      * @throws \Exception
      */
     public static function updateSharedFolder(SharedFolder $folder, array $props = []): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         $settings = $folder->getSettings(['acl', 'folder']);
         $acl = !empty($settings['acl']) ? json_decode($settings['acl'], true) : null;
         $folder = $settings['folder'];
         $mailbox = self::toUTF7($folder);
 
         // Rename the mailbox
         if (!empty($props['folder']) && $props['folder'] != $folder) {
             $oldMailbox = self::toUTF7($props['folder']);
 
             if (!$imap->renameFolder($oldMailbox, $mailbox)) {
                 \Log::error("Failed to rename mailbox {$oldMailbox} to {$mailbox}");
                 $imap->closeConnection();
                 return false;
             }
         }
 
         // Note: Shared folder type does not change
 
         // ACL
         self::aclUpdate($imap, $mailbox, $acl);
 
         $imap->closeConnection();
 
         return true;
     }
 
     /**
      * Delete a shared folder.
      *
      * @param \App\SharedFolder $folder Shared folder
      *
      * @return bool True if a falder was deleted successfully, False otherwise
      * @throws \Exception
      */
     public static function deleteSharedFolder(SharedFolder $folder): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         $settings = $folder->getSettings(['folder']);
         $mailbox = self::toUTF7($settings['folder']);
 
         // To delete the mailbox cyrus-admin needs extra permissions
         $imap->setACL($mailbox, $config['user'], 'c');
 
         // Delete the mailbox
         $result = $imap->deleteFolder($mailbox);
 
         $imap->closeConnection();
 
         return $result;
     }
 
     /**
      * Check if a shared folder is set up.
      *
      * @param string $folder Folder name, e.g. shared/Resources/Name@domain.tld
      *
      * @return bool True if a folder exists and is set up, False otherwise
      */
     public static function verifySharedFolder(string $folder): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         // Convert the folder from UTF8 to UTF7-IMAP
         if (\preg_match('#^(shared/|shared/Resources/)(.+)(@[^@]+)$#', $folder, $matches)) {
             $folderName = self::toUTF7($matches[2]);
             $folder = $matches[1] . $folderName . $matches[3];
         }
 
         // FIXME: just listMailboxes() does not return shared folders at all
 
         $metadata = $imap->getMetadata($folder, ['/shared/vendor/kolab/folder-type']);
 
         $imap->closeConnection();
 
         // Note: We have to use error code to distinguish an error from "no mailbox" response
 
         if ($imap->errornum === \rcube_imap_generic::ERROR_NO) {
             return false;
         }
 
         if ($imap->errornum !== \rcube_imap_generic::ERROR_OK) {
             throw new \Exception("Failed to get folder metadata from IMAP");
         }
 
         return true;
     }
 
     /**
      * Convert UTF8 string to UTF7-IMAP encoding
      */
     public static function toUTF7(string $string): string
     {
         return \mb_convert_encoding($string, 'UTF7-IMAP', 'UTF8');
     }
 
     /**
      * Check if an account is set up
      *
      * @param string $username User login (email address)
      *
      * @return bool True if an account exists and is set up, False otherwise
      */
     public static function verifyAccount(string $username): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         $mailbox = self::toUTF7('user/' . $username);
 
         // Mailbox already exists
         if (self::folderExists($imap, $mailbox)) {
             $imap->closeConnection();
             return true;
         }
 
         $imap->closeConnection();
         return false;
     }
 
     /**
      * Check if an account is set up
      *
      * @param string $username User login (email address)
      *
      * @return bool True if an account exists and is set up, False otherwise
      */
     public static function verifyDefaultFolders(string $username): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config, $username);
 
         foreach (\config('imap.default_folders') as $mb => $_metadata) {
             $mailbox = self::toUTF7($mb);
             if (!self::folderExists($imap, $mailbox)) {
                 $imap->closeConnection();
                 return false;
             }
         }
 
         $imap->closeConnection();
         return true;
     }
 
     /**
      * Check if we can connect to the imap server
      *
      * @return bool True on success
      */
     public static function healthcheck(): bool
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
         $imap->closeConnection();
         return true;
     }
 
     /**
      * Remove ACL for a specified user/group anywhere in the IMAP
      *
      * @param string $ident  ACL identifier (user email or e.g. group name)
      * @param string $domain ACL domain
      */
     public static function aclCleanup(string $ident, string $domain = ''): void
     {
         $config = self::getConfig();
         $imap = self::initIMAP($config);
 
         if (strpos($ident, '@')) {
             $domain = explode('@', $ident, 2)[1];
         }
 
         $callback = function ($folder) use ($imap, $ident) {
             $acl = $imap->getACL($folder);
             if (is_array($acl) && isset($acl[$ident])) {
                 $imap->deleteACL($folder, $ident);
             }
         };
 
         $folders = $imap->listMailboxes('', "user/*@{$domain}");
 
         if (!is_array($folders)) {
             $imap->closeConnection();
             throw new \Exception("Failed to get IMAP folders");
         }
 
         array_walk($folders, $callback);
 
         $folders = $imap->listMailboxes('', "shared/*@{$domain}");
 
         if (!is_array($folders)) {
             $imap->closeConnection();
             throw new \Exception("Failed to get IMAP folders");
         }
 
         array_walk($folders, $callback);
 
         $imap->closeConnection();
     }
 
     /**
      * Create a folder and set some default properties
      *
      * @param \rcube_imap_generic $imap The imap instance
      * @param string $mailbox Mailbox name
      * @param bool $subscribe Subscribe to the folder
      * @param array $metadata Metadata to set on the folder
      * @param array $acl Acl to set on the folder
      *
      * @return bool True when having a folder created, False if it already existed.
      * @throws \Exception
      */
     private static function createFolder($imap, string $mailbox, $subscribe = false, $metadata = null, $acl = null)
     {
         if (self::folderExists($imap, $mailbox)) {
             return false;
         }
 
         if (!$imap->createFolder($mailbox)) {
             throw new \Exception("Failed to create mailbox {$mailbox}");
         }
 
         if ($acl) {
             self::aclUpdate($imap, $mailbox, $acl, true);
         }
 
         if ($subscribe) {
             $imap->subscribe($mailbox);
         }
 
         foreach ($metadata as $key => $value) {
             $imap->setMetadata($mailbox, [$key => $value]);
         }
 
         return true;
     }
 
     /**
      * Convert Kolab ACL into IMAP user->rights array
      */
     private static function aclToImap($acl): array
     {
         if (empty($acl)) {
             return [];
         }
 
         return \collect($acl)
             ->mapWithKeys(function ($item, $key) {
                 list($user, $rights) = explode(',', $item, 2);
                 return [trim($user) => self::ACL_MAP[trim($rights)]];
             })
             ->all();
     }
 
     /**
      * Update folder ACL
      */
     private static function aclUpdate($imap, $mailbox, $acl, bool $isNew = false)
     {
         $imapAcl = $isNew ? [] : $imap->getACL($mailbox);
 
         if (is_array($imapAcl)) {
             foreach (self::aclToImap($acl) as $user => $rights) {
                 if (empty($imapAcl[$user]) || implode('', $imapAcl[$user]) !== $rights) {
                     $imap->setACL($mailbox, $user, $rights);
                 }
 
                 unset($imapAcl[$user]);
             }
 
             foreach ($imapAcl as $user => $rights) {
                 $imap->deleteACL($mailbox, $user);
             }
         }
     }
 
     /**
      * Check if an IMAP folder exists
      */
     private static function folderExists($imap, string $folder): bool
     {
         $folders = $imap->listMailboxes('', $folder);
 
         if (!is_array($folders)) {
             $imap->closeConnection();
             throw new \Exception("Failed to get IMAP folders");
         }
 
         return count($folders) > 0;
     }
 
     /**
      * Initialize connection to IMAP
      */
     private static function initIMAP(array $config, string $login_as = null)
     {
         $imap = new \rcube_imap_generic();
 
         if (\config('app.debug')) {
             $imap->setDebug(true, 'App\Backends\IMAP::logDebug');
         }
 
         if ($login_as) {
             $config['options']['auth_cid'] = $config['user'];
             $config['options']['auth_pw'] = $config['password'];
             $config['options']['auth_type'] = 'PLAIN';
             $config['user'] = $login_as;
         }
 
         $imap->connect($config['host'], $config['user'], $config['password'], $config['options']);
 
         if (!$imap->connected()) {
             $message = sprintf("Login failed for %s against %s. %s", $config['user'], $config['host'], $imap->error);
 
             \Log::error($message);
 
             throw new \Exception("Connection to IMAP failed");
         }
 
         return $imap;
     }
 
     /**
      * Get LDAP configuration for specified access level
      */
     private static function getConfig()
     {
         $uri = \parse_url(\config('imap.uri'));
         $default_port = 143;
         $ssl_mode = null;
 
         if (isset($uri['scheme'])) {
             if (preg_match('/^(ssl|imaps)/', $uri['scheme'])) {
                 $default_port = 993;
                 $ssl_mode = 'ssl';
             } elseif ($uri['scheme'] === 'tls') {
                 $ssl_mode = 'tls';
             }
         }
 
         $config = [
             'host' => $uri['host'],
             'user' => \config('imap.admin_login'),
             'password' => \config('imap.admin_password'),
             'options' => [
                 'port' => !empty($uri['port']) ? $uri['port'] : $default_port,
                 'ssl_mode' => $ssl_mode,
                 'socket_options' => [
                     'ssl' => [
                         'verify_peer' => \config('imap.verify_peer'),
                         'verify_peer_name' => \config('imap.verify_peer'),
                         'verify_host' => \config('imap.verify_host')
                     ],
                 ],
             ],
         ];
 
         return $config;
     }
 
     /**
      * Debug logging callback
      */
     public static function logDebug($conn, $msg): void
     {
         $msg = '[IMAP] ' . $msg;
 
         \Log::debug($msg);
     }
 }