Mail delivery failed: returning message to sender errors are generally encountered when an intended recipient does not exist on the remote server.

You will normally receive a bounceback message with this error in the subject, and the body of the message should contain the original message that was attempting to be sent.

Example bounce-back message

Return-path: <>
Delivery-date: Thu, 25 Oct 2012 16:42:54 -0400
Received: from mailnull by with local (Exim 4.77)
id 1TRUGT-0005Qd-RT
for; Thu, 25 Oct 2012 16:42:54 -0400
Auto-Submitted: auto-replied
From: Mail Delivery System <>
Subject: Mail delivery failed: returning message to sender
Message-Id: <>
Date: Thu, 25 Oct 2012 16:42:53 -0400

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:
No Such User Here
------ This is a copy of the message, including all the headers. ------
Return-path: <>
Received: from by with local (Exim 4.77)
(envelope-from <>)
id 1TRUGT-0005QT-Q5
for; Thu, 25 Oct 2012 16:42:53 -0400
Subject: [] Please moderate: "About us"
X-PHP-Script: for
Date: Thu, 25 Oct 2012 20:42:53 +0000
From: WordPress <>
Message-ID: <>
X-Priority: 3
X-Mailer: PHPMailer 5.1 (
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain; charset="UTF-8"
A new comment on the post "About us" is waiting for your approval
Author : Payday loans (IP:
E-mail :
Comment: Payday loans are available for any occasion! 

Resolving Mail delivery failed: returning message to sender bounce-backs

Typically these type of bounceback errors are hard bounces meaning that trying to send the message again won't be successful. You can read our previous article on why does email bounce, bounceback, or error? for a more in-depth explanation of a hard bounce.

In the particular bounce-back example above, the cause of the issue is that this user has WordPress setup to allow comments on posts. A spammer attempted to leave a comment on one of their posts, and the WordPress administrator of this site has setup their e-mail account as So that is the address used to send comment moderation requests to. However that e-mail address doesn't exist on the mail server, so it's always going to fail and cause a bounce-back error.

If you happen to also be having issues with WordPress comment spam causing bounce-back errors for your account, we have an advanced article on WordPress comment spam clean up that could help you clear this issue up.

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n/a Points
2014-09-13 5:46 am


   Thank you for the suggestions.  I had tried "add that particular address to the blocked list", but it didn't work.  I've resolved the problem now.  It was a scorpion virus. I had to pay Norton $99 to uninstall/reinstall Norton antivirus and change my password. 

   Again, thank you for your suggestion.

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