diff --git a/framework/Core/lib/Horde/Core/ActiveSync/Connector.php b/framework/Core/lib/Horde/Core/ActiveSync/Connector.php
index fdb6b97adcb..345dccee069 100644
--- a/framework/Core/lib/Horde/Core/ActiveSync/Connector.php
+++ b/framework/Core/lib/Horde/Core/ActiveSync/Connector.php
@@ -294,6 +294,32 @@ public function calendar_move($uid, $source, $target)
         return $uid;
     }
 
+    /**
+     * Return an event attachment.
+     *
+     * @param string $filereference  A filereference pointing to the file:
+     *                           calendar:{calendar_id}:{event_uid}:{filename}
+     *
+     * @return array  An array containing:
+     *                   'content-type' and 'data'.
+     */
+    public function calendar_getAttachment($filereference)
+    {
+        if (!$this->_registry->hasMethod(
+            'getAttachment',
+            $this->_registry->hasInterface('calendar'))) {
+            return false;
+        }
+        $fileinfo = explode(':', $filereference, 4);
+        try {
+            return $this->_registry->calendar->getAttachment(
+                $fileinfo[1], $fileinfo[2], $fileinfo[3]
+            );
+        } catch (Horde_Exception $e) {
+            return false;
+        }
+    }
+
     /**
      * Get a list of all contacts a user can see
      *
diff --git a/framework/Core/lib/Horde/Core/ActiveSync/Driver.php b/framework/Core/lib/Horde/Core/ActiveSync/Driver.php
index 96fe843d85a..ffcd823d145 100644
--- a/framework/Core/lib/Horde/Core/ActiveSync/Driver.php
+++ b/framework/Core/lib/Horde/Core/ActiveSync/Driver.php
@@ -1559,7 +1559,22 @@ public function itemOperationsFetchMailbox(
      */
     public function itemOperationsGetAttachmentData($filereference)
     {
-        $att = $this->getAttachment($filereference);
+        // @todo Slight issue here. Since the filereferences that had previously
+        // been returned to the client for email attachments only contain
+        // the mailbox name/uid/part of the message, leaving things as-is would
+        // mean that a mailbox named 'calendar' would break this code.
+        // To deal with that cleanly, we really need to prepend 'mail'
+        // to all email attachments, but this would require a resync of all
+        // clients to be sure the new filereferences are sent. For now, do
+        // some sniffing to try to figure it out.
+        //
+        // Calendar would have 4 parts, so check that first.
+        $name_parts = explode(':', $filereference, 4);
+        if ($name_parts[0] == 'calendar' && !empty($name_parts[3])) {
+            $att = $atc = $this->_connector->calendar_getAttachment($filereference);
+        } else {
+            $att = $this->getAttachment($filereference);
+        }
         $airatt = Horde_ActiveSync::messageFactory('AirSyncBaseFileAttachment');
         $airatt->data = $att['data'];
         $airatt->contenttype = $att['content-type'];
@@ -1816,8 +1831,12 @@ public function moveMessage($folderid, array $ids, $newfolderid)
      *   Contains the following keys:
      *   - id: (mixed)  The UID of the message/item.
      *   - mod: (mixed) A value to indicate the last modification.
-     *   - flags: (array) an empty array if no flag changes.
-     *   - categories: (array|boolean) false if no changes.
+     *   - flags: (array) An array of flag chagnes, empty array if no changes.
+     *   - categories: (array|boolean) An array of EAS categories for email
+     *        messages that exist as IMAP flags, false if no changes.
+     *   - atchash: (array|boolean) An array of clientid->filereference
+     *         mappings for file attachment changes made to appointment
+     *         or draft email folders. @since 2.27.0
      */
     public function changeMessage($folderid, $id, Horde_ActiveSync_Message_Base $message, $device)
     {
@@ -1849,25 +1868,37 @@ public function changeMessage($folderid, $id, Horde_ActiveSync_Message_Base $mes
         case Horde_ActiveSync::CLASS_CALENDAR:
             if (!$id) {
                 try {
-                    $id = $this->_connector->calendar_import($message, $server_id);
+                    // @todo, remove 'import16' hack for H6
+                    $results  = $this->_connector->calendar_import16($message, $server_id);
                 } catch (Horde_Exception $e) {
                     $this->_logger->err($e->getMessage());
                     $this->_endBuffer();
                     return false;
                 }
-                $stat = array('mod' => $this->getSyncStamp($folderid), 'id' => $id, 'flags' => 1);
+                $stat = array(
+                    'mod' => $this->getSyncStamp($folderid),
+                    'id' => $results['uid'],
+                    'flags' => 1,
+                    'atchash' => $results['atchash']
+                );
             } else {
                 // ActiveSync messages do NOT contain the serverUID value, put
                 // it in ourselves so we can have it during import/change.
                 $message->setServerUID($id);
                 try {
-                    $this->_connector->calendar_replace($id, $message, $server_id);
+                    $results = $this->_connector->calendar_replace($id, $message, $server_id);
                 } catch (Horde_Exception $e) {
                     $this->_logger->err($e->getMessage());
                     $this->_endBuffer();
                     return false;
                 }
                 $stat = $this->_smartStatMessage($folderid, $id, false);
+                // @todo Remove this check in H6, when the API always returns.
+                if (!empty($results)) {
+                    $stat['atchash'] = !empty($results['atchash'])
+                        ? $results['atchash']
+                        : false;
+                }
             }
             break;