Index: CHANGELOG
===================================================================
--- CHANGELOG	(revision b46e5b7407940499964d8a553c3eada05850f29d)
+++ CHANGELOG	(revision 99897b7c4e52a5ff026c3828b84653f460f571f0)
@@ -4,4 +4,7 @@
 RELEASE 0.5.1
 -------------
+- Fix handling of attachments with invalid content type (#1487767)
+- Add workaround for DBMail's bug http://www.dbmail.org/mantis/view.php?id=881 (#1487766)
+- Use IMAP's ID extension (RFC2971) to print more info into debug log
 - Security: add optional referer check to prevent CSRF in GET requests
 - Fix email_dns_check setting not used for identities/contacts (#1487740)
Index: program/include/rcube_imap.php
===================================================================
--- program/include/rcube_imap.php	(revision 98cb0f179206843ceaa87df6bfb3d1da045ed8ad)
+++ program/include/rcube_imap.php	(revision 99897b7c4e52a5ff026c3828b84653f460f571f0)
@@ -149,6 +149,15 @@
         $this->options['port'] = $port;
 
-        if ($this->options['debug'])
+        if ($this->options['debug']) {
             $this->conn->setDebug(true, array($this, 'debug_handler'));
+
+            $this->options['ident'] = array(
+                'name' => 'Roundcube Webmail',
+                'version' => RCMAIL_VERSION,
+                'php' => PHP_VERSION,
+                'os' => PHP_OS,
+                'command' => $_SERVER['REQUEST_URI'],
+            );
+        }
 
         $attempt = 0;
Index: program/include/rcube_imap_generic.php
===================================================================
--- program/include/rcube_imap_generic.php	(revision b46e5b7407940499964d8a553c3eada05850f29d)
+++ program/include/rcube_imap_generic.php	(revision 99897b7c4e52a5ff026c3828b84653f460f571f0)
@@ -760,4 +760,9 @@
         }
 
+        // Send ID info
+        if (!empty($this->prefs['ident']) && $this->getCapability('ID')) {
+            $this->id($this->prefs['ident']);
+        }
+
         $auth_methods = array();
         $result       = null;
@@ -1153,4 +1158,42 @@
         if (is_array($index)) {
             return (int) $index['COUNT'];
+        }
+
+        return false;
+    }
+
+    /**
+     * Executes ID command (RFC2971)
+     *
+     * @param array $items Client identification information key/value hash
+     *
+     * @return array Server identification information key/value hash
+     * @access public
+     * @since 0.6
+     */
+    function id($items=array())
+    {
+        if (is_array($items) && !empty($items)) {
+            foreach ($items as $key => $value) {
+                $args[] = $this->escape($key);
+                $args[] = $this->escape($value);
+            }
+        }
+
+        list($code, $response) = $this->execute('ID', array(
+            !empty($args) ? '(' . implode(' ', (array) $args) . ')' : $this->escape(null)
+        ));
+
+
+        if ($code == self::ERROR_OK && preg_match('/\* ID /i', $response)) {
+            $response = substr($response, 5); // remove prefix "* ID "
+            $items    = $this->tokenizeResponse($response);
+            $result   = null;
+
+            for ($i=0, $len=count($items); $i<$len; $i += 2) {
+                $result[$items[$i]] = $items[$i+1];
+            }
+
+            return $result;
         }
 
@@ -3285,8 +3328,9 @@
             return '""';
         }
+        // need quoted-string? find special chars: SP, CTL, (, ), {, %, *, ", \, ]
+        // plus [ character as a workaround for DBMail's bug (#1487766)
         else if ($force_quotes ||
-            preg_match('/([\x00-\x20\x28-\x29\x7B\x25\x2A\x22\x5C\x5D\x7F]+)/', $string)
+            preg_match('/([\x00-\x20\x28-\x29\x7B\x25\x2A\x22\x5B\x5C\x5D\x7F]+)/', $string)
         ) {
-            // string: special chars: SP, CTL, (, ), {, %, *, ", \, ]
             return '"' . strtr($string, array('"'=>'\\"', '\\' => '\\\\')) . '"';
         }
Index: program/include/rcube_message.php
===================================================================
--- program/include/rcube_message.php	(revision b46e5b7407940499964d8a553c3eada05850f29d)
+++ program/include/rcube_message.php	(revision 99897b7c4e52a5ff026c3828b84653f460f571f0)
@@ -479,8 +479,19 @@
                             $this->attachments[] = $mail_part;
                     }
-                    // is a regular attachment (content-type name regexp according to RFC4288.4.2)
+                    // regular attachment with valid content type
+                    // (content-type name regexp according to RFC4288.4.2)
                     else if (preg_match('/^[a-z0-9!#$&.+^_-]+\/[a-z0-9!#$&.+^_-]+$/i', $part_mimetype)) {
                         if (!$mail_part->filename)
                             $mail_part->filename = 'Part '.$mail_part->mime_id;
+
+                        $this->attachments[] = $mail_part;
+                    }
+                    // attachment with invalid content type
+                    // replace malformed content type with application/octet-stream (#1487767)
+                    else if ($mail_part->filename) {
+                        $mail_part->ctype_primary   = 'application';
+                        $mail_part->ctype_secondary = 'octet-stream';
+                        $mail_part->mimetype        = 'application/octet-stream';
+
                         $this->attachments[] = $mail_part;
                     }