AOL will not accept delivery of this message

We’re using MIAB for our business’s email. Perhaps this isn’t the “best” option for business purposes, but it works great for me.

Anyways, most (if not all) of our emails to AOL customers are being blocked, saying: host[] said: 521 5.2.1 :
AOL will not accept delivery of this message. (in reply to end of DATA

Looking at AOL’s site, this can be caused by:

  • RFC2822 From domain does not match the rDNS of sending server.
  • RFC 2822 FROM address does not have an A record and is not a valid domain.
  • IP has a poor reputation and mail is sent to multiple recipients.
  • There are multiple From address in the mail headers and the IP reputation is poor.

I’ve contacted them via their ticket system several times with minimal response. One person replied saying the did something on their end to fix it, but I continue to receive bounces. (I wish I had some sort of leverage!)

Anyways, since I’m receiving little help from AOL, I was wondering if you guys could think of anything? My boss is getting quite paranoid and I don’t know what else to do :scream:. Ideas? Thanks guys!

Host is

Here’s one of the (censored) bounces:

Return-Path: <>
Delivered-To: <>
Received: from ([])
	by (Dovecot) with LMTP id iQiDKu2F7lk8PQAAGC+CJg
	for <>; Mon, 23 Oct 2017 20:14:40 -0400
X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on
X-Spam-Status: No, score=0.0 required=5.0 tests=HTML_MESSAGE,NO_RELAYS
	autolearn=ham autolearn_force=no version=3.4.0
	* -0.0 NO_RELAYS Informational: message was not relayed via SMTP
	*  0.0 HTML_MESSAGE BODY: HTML included in message
Received: by (Postfix)
	id 35714236FB; Mon, 23 Oct 2017 20:14:40 -0400 (EDT)
Date: Mon, 23 Oct 2017 20:14:40 -0400 (EDT)
From: (Mail Delivery System)
Subject: Undelivered Mail Returned to Sender
Auto-Submitted: auto-replied
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
Message-Id: <>

This is a MIME-encapsulated message.

Content-Description: Notification
Content-Type: text/plain; charset=us-ascii

This is the mail system at host

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<>: host[] said: 521 5.2.1 :
    AOL will not accept delivery of this message. (in reply to end of DATA

Content-Description: Delivery report
Content-Type: message/delivery-status

Reporting-MTA: dns;
X-Postfix-Queue-ID: 853C6207E0
X-Postfix-Sender: rfc822;
Arrival-Date: Mon, 23 Oct 2017 20:14:37 -0400 (EDT)

Final-Recipient: rfc822;
Original-Recipient: rfc822;
Action: failed
Status: 5.2.1
Remote-MTA: dns;
Diagnostic-Code: smtp; 521 5.2.1 :  AOL will not accept delivery of this

Content-Description: Undelivered Message
Content-Type: message/rfc822

Return-Path: <>
Received: from authenticated-user ( [])
	(using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits))
	(No client certificate requested)
	by (Postfix) with ESMTPSA id 853C6207E0;
	Mon, 23 Oct 2017 20:14:37 -0400 (EDT)
DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple;;
	s=mail; t=1508804077;
Date: Tue, 24 Oct 2017 00:14:36 +0000
Subject: Submission Received
Message-ID: <>
MIME-Version: 1.0
Content-Type: text/html; charset=iso-8859-1

<div style="font-family:Arial, Helvetica, sans-serif; font-size:10pt; width:600px;">
<p>Dear xxx,<br/><br />
			xxxxxxx<br/><br />
			Please keep this email as a receipt of your gift:<br/><br />
			Type: Credit Card<br />
			Appeal: xxxxxxx<br />
			Support-Us <br />
			Amount: $xxx.xx<br/><br />
			        <br/><br />
			Status: APPROVED<br />Message: AUTH/TKT<br />Appeal: Support-Us <br />Transaction ID: xxxxxx<br />AVS Response: Y<br />CVS Response: S<br />Masked Account: xxxxxxxxxxxxxxxx<br />Card Type: xxx<br />Authorization Code: xxx<br /><br/><br />
			To register your account and access your giving history online, please <a href='xxxxx'>click here</a>. Registration is optional. By registering, you will be able to access an end-of-year giving statement for the prior year to be used for tax purposes.<br/><br />
			Please note that your email address will only be used to service your GivingTools account and will not be sold, transferred, or used for any other purpose.<br/><br />
			Thank you again for your generous gift.<br/><br />
			&#8212;xxxx</p><br />


Most likely, “IP reputation is poor” is a major, if not THE, factor. Are there multiple recipients or return addresses?

Please read:

I hoped AOL would tell me my reputation, but it says “undisclosed” :frowning:

I believe there is only one recipient (one To header?).

But…I think fixing it by tweaking various things like the www in the Message-ID, Reply-To being equal to the To header, adding a text alternative, and adding doctype and html tags as necessary.

I saw one AOL email go through with these changes, so it might have helped.

Regardless, we’re going to setup Mailgun as a SMTP relay for all our email. I’m sure we won’t have any problems with this in place!