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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.

n/a Points
2015-03-24 7:21 am


Can you give advice in solving my problem regarding:


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 end of data:

host [2a00:1450:4013:c01::1b]:

550-5.7.1 [2a01:5b40:0:252::55      12] Our system has detected that this

550-5.7.1 message is likely unsolicited mail. To reduce the amount of spam sent

 550-5.7.1 to Gmail, this message has been blocked. Please visit

 550-5.7.1 for

550 5.7.1 more information. w1si16472613wix.3 - gsmtp

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


19,030 Points
2015-03-24 8:54 am
Hello Jorunn,

Thank you for your question. The content of this email message is being flagges bu Google as spam.

The link you provided, included more in-depth information from Google.

I recommend avoiding common words that trigger spam filters.

Also, SPF records and Domain Keys can verify your emails are being sent un-tampered from a valid server.

Thank you,
n/a Points
2015-08-04 1:14 pm


I've been getting emails back from email addresses I know are coorect. Why?

Some are from an email message I send to multiple recipeints and some are to just one and I get the mailer daemon message as well.




5,833 Points
2015-08-04 11:42 pm
Hello Sara,

Can you please provide the headers of one of the bounce back messages so we may decipher what the issue at hand may be and possibly a resolution.

Best Regards.
TJ Edens
n/a Points
2015-08-14 8:09 pm



Since yesterday, when someone sends me an email to  they receive a mail delivery failed message, but I do receive their email. See below the message

*removed by moderator for identifying information*
30,216 Points
2015-08-17 9:55 am
Hello Renato,

If you are one of our customers, you may want to check with out Live Support team to see what is wrong with your specific account. That is not normal server behavior.

Kindest Regards,
Scott M
2015-09-10 3:29 am
it seems that your local IP address does not have a valid reverse DNS in which your mail has been authenticating.

So kindly contact your local internet provider to add the valid reverse DNS else try with any other internet provider.
19,030 Points
2015-09-10 9:58 am
Hello saravananct,

Thank you for contacting us. Since we do not own that IP address we cannot setup the reverse DNS for you. I recommend contacting your host, so they can assist you with this configuration.

Thank you,

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