Frequently asked questions


What does 'Mail delivery failed: returning message to sender' mean?

If you try to send an email and then receive an email in return with the subject: Mail delivery failed: returning message to sender. It means the email was not delivered.

This return mail contains a lot of technical information, but if you know what to look for, you can easily find out the reason to why it was not delivered.

This is an example of such an email:

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:
    SMTP error from remote mail server after RCPT TO::
 host [2a01:5b40:0:2204::1]:
    553 5.3.0 ... No such user here

------ This is a copy of the message, including all the headers. ------

Received: from [2a01:5b40:0:253::24] (port=64430)
	by with esmtpsa (TLS1.2:DHE_RSA_AES_128_CBC_SHA1:128)
	(Exim 4.80)
	(envelope-from )
	id 1bRcGB-0006Jf-RM
	for; Mon, 25 Jul 2016 11:33:15 +0200
From: Ola Nordmann 
Subject: test
Message-ID: <>
Date: Mon, 25 Jul 2016 11:33:13 +0200
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit

We have marked which server submitted the error message and what the error message is, in the color red.

This line tells you which server submitted the error message:

host [2a01:5b40:0:2204::1]

This line is the error message itself.

553 5.3.0 ... No such user here
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