2015-08-04 | 5549 Print PDF
Although I have had my fair share of spam over the years, I have never had this problem before. Mail delivery failed: returning message to sender errors are generally encountered when an intended recipient does not exist on the remote server or you have exceeded the maximum number of failed mail delivery.
Within last week, I have started receiving hundreds of "bounced" email messages; and other such as "out of office" ones from email accounts that actually exist.
Have not been recently hacked nor has my email account got into the wrong hands, I do not have a WordPress site (since hackers can easily inject such trojans into server via FREE Word press themes downloads) that has been hacked, So what might be the issue?
You will normally receive a bounce back message with this error in the subject, and the body of the message should contain the original message that was attempting to be sent.
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: firstname.lastname@example.org host yourdomain.net [18.104.22.168] SMTP error from remote mail server after end of data: 550-DKIM: encountered the following problem validating seowebanalyst.com: 550 pubkey_unavailable
Another type of Mail Delivery FAILED is one from popular email providers like Gmail, Yahoo!, Microsoft, AOL, etc
They provide such errors like
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 aspmx.l.google.com [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 more information. w1si16472613wix.3 - gsmtp
------ This is a copy of the message, including all the headers. ------
The basic reason for this Message Delivery error is because the content of this email message is being flagged by Google as spam.
The link you provided, included more in-depth information from Google. I will 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.
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: email@example.com Domain mydomain.com has exceeded the max defers and failures per hour (5/5 (100%)) allowed. Message discarded.
You are facing a cPanel restriction in order to prevent spam in the server. This happens when you or one of your clients have frequently sent emails to invalid or non-existent email accounts and
the percentage of bounced emails have reached its limit per hosting account.
cPanel will regularly monitor the emails sent through all email accounts on your domain, and if, over the past hour, more than 25% of the attempted deliveries have failed, outbound email will temporarily be limited.
The "(5/5)" portion of the error indicates that the measurement of bounces kicked in once 5 bounces were detected during the hour. In other words, if you have 4 bounces in an hour during which you sent 16 emails, even though 50% of your emails have bounced, nothing will happen because you are under 5 bounces. Once you reach five bounces in an hour, the bounce percentage measurement is taken and a sending restriction is enforced if you're over the bounce percentage limit.
Because there are clients who fail to keep their PHP scripts updated with newest versions, some sites are vulnerable to exploits by spammers. Sites get hacked and mail accounts hijacked for spam purposes. Because spam campaigns have a high bounce rate, this feature can quickly limit the damage that can be done by these exploits, and prevent our servers from ending up on dns blacklists, and then being unable to deliver legitimate email properly.
The server will block the mail activity for the last one hour. You need stop sending email in one hour. Then the server will remove the block automatically.
You might also be interested to read How To Stop Spam Emails In Cpanel