Send a dummy OUTBOX folder to work around broken clients.

Some client evidently try to synchronize the Outbox, even when
no such folder is sent via the FOLDERSYNC response. Try to avoid
this issue by sending a mailbox with the SPECIAL_OUTBOX indicator.

framework/Core/lib/Horde/Core/ActiveSync/Driver.php

@@ -1114,7 +1114,8 @@ public function getServerChanges(
             break;
 
         case Horde_ActiveSync::CLASS_EMAIL:
-            if (empty($this->_imap)) {
+            if (empty($this->_imap) ||
+                $folder->serverid() == 'OUTBOX') {
                 $this->_endBuffer();
                 return array();
             }
@@ -1814,6 +1815,12 @@ public function changeMessage($folderid, $id, Horde_ActiveSync_Message_Base $mes
             $this->_pid,
             $folderid,
             $id));
+
+        // Short circuit OUTBOX modifications to work around broken clients.
+        if ($folderid == 'OUTBOX') {
+            return false;
+        }
+
         ob_start();
 
         $folder_split = $this->_parseFolderId($folderid);
@@ -3088,6 +3095,9 @@ protected function _getMailFolders()
                     ++$level;
                 }
 
+                // Fake Outbox for broken clients.
+                $folders[] = $this->_buildDummyFolder(self::SPECIAL_OUTBOX);
+
                 $this->_mailFolders = $folders;
             }
         }