support message delivery status (#47)

Author: eidng8

src/IMAP/Message.php

@@ -431,6 +431,9 @@ private function fetchStructure($structure, $partNumber = null) {
      */
     protected function fetchAttachment($structure, $partNumber){
         switch ($structure->type) {
+            case self::TYPE_MESSAGE:
+                $type = 'message';
+                break;
             case self::TYPE_APPLICATION:
                 $type = 'application';
                 break;
@@ -476,6 +479,13 @@ protected function fetchAttachment($structure, $partNumber){
                 }
             }
         }
+        if(self::TYPE_MESSAGE == $structure->type) {
+            if($structure->ifdescription) {
+                $attachment->name = $structure->description;
+            } else {
+                $attachment->name = $structure->subtype;
+            }
+        }
 
         if (!$attachment->name && property_exists($structure, 'parameters')) {
             foreach ($structure->parameters as $parameter) {