Parse disposition-notification-to header as address (#359)

Author: RoyalBingBong

lib/mail-parser.js

@@ -365,6 +365,7 @@ class MailParser extends Transform {
                 case 'reply-to':
                 case 'delivered-to':
                 case 'return-path':
+                case 'disposition-notification-to':
                     value = addressparser(value);
                     this.decodeAddresses(value);
                     value = {
@@ -409,7 +410,8 @@ class MailParser extends Transform {
             'mime-version',
             'content-description',
             'precedence',
-            'errors-to'
+            'errors-to',
+            'disposition-notification-to'
         ];
 
         headers.forEach((value, key) => {