В случае отсутствия почтового ящика на указанном сервере, признания входящего письма спамом отправитель получает ответы от почтового сервера вида:

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  user1@domain.com
    host mail.domain.com [000.000.000.000]
    SMTP error from remote mail server after RCPT TO:<user1@domain.com>:
    550 5.1.1 <user1@domain.com>: Recipient address rejected:
    User unknown in virtual mailbox table

 

 

Reporting-MTA: dns; mail.domain.com

Action: failed
Final-Recipient: rfc822;user1@domain.com
Status: 5.0.0
Remote-MTA: dns; mail.domain.com
Diagnostic-Code: smtp; 550 5.1.1 <user1@domain.com>: Recipient address rejected: User unknown in virtual mailbox table

 

 

Return-path: <user2@domain.com>
Received: from [111.111.111.111] (helo=user2.local)
	by mail.domain.com with esmtpa (Exim (OS))
	(envelope-from <user2@domain.com>)
	id 1fEZ5J-000KnB-Ow
	for user1@domain.com; Fri, 04 May 2018 14:41:10 +0300
To: =?UTF-8?B?0JrQu9GO0LXQsiDQkNC90LTRgNC10Lkg0JLQsNC70LXRgNGM0LXQstC40Yc=?=
 <user1@domain.com>
From: =?UTF-8?B?0JXQstC00L7QutC40LzQvtCyINCd0LjQutC+0LvQsNC5?=
 <user2@domain.com>
Subject: test
Message-ID: <436d6217-a5db-acf7-dd57-2c03b67cf88b@sushivesla.su>
Date: Fri, 4 May 2018 14:41:09 +0300
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0)
 Gecko/20100101 Thunderbird/52.7.0
MIME-Version: 1.0
Content-Type: multipart/alternative;
 boundary="------------B98126044474707661523413"
Content-Language: ru
X-Exim-DSN-Information: Due to administrative limits only headers are returned

А хотелось бы видеть что то более удобочитаемое для пользователя.
Кто нибудь побеждал такую задачу?
Подскажите с какой стороны начать копать.