How to resolve “Sender verify failed” SMTP mail error in cPanel/WHM Exim servers

How to resolve “Sender verify failed” SMTP mail error in cPanel/WHM Exim servers

SMTP error from remote mail server after RCPT TO:<user2@domain2.com>:
host mx.server.com [xxx.xxx.xxx.xxx]: 550-Verification failed for <user1@domain1.com>
550-No Such User Here
550 Sender verify failed

Bobcares provides website management services to website owners. Email errors are the most commonly encountered issues by the end customers.

Amongst these mail errors, ‘Sender verify failed’ is a prominent error that creates so much hassle to account owners. We’ve seen that it can be caused by issues ranging from improper file permissions to RFC non-compliance.

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Email errors can be troublesome for any website owner, as it can affect your marketing campaign or delay an urgent business or personal mail indefinitely. Delay or loss of emails can cause financial loss and stress.

The error message ‘Sender verify failed’, if a very confusing one for many website owners, as it can be caused due to several reasons, unrelated to each other.

From our experience managing hundreds of cPanel servers in our role as Website Support Techs for web hosting companies, we’ve figured out 3 major causes for this error.

  1. Email account doesn’t exist or cannot be detected
  2. Duplicate sender account in recipient server
  3. Misconfigured mail exchanger

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1. Email account doesn’t exist or cannot be detected

The ‘Sender Verify’ or ‘Callback Verification’ is an antispam feature in mail servers. For a user to be able to send a mail through a cPanel/WHM server, the sending email address should be present and active in the server.

If the mail server is unable to verify the sender address, it will reject the email with the error message ‘550 Sender verify failed’. In cPanel servers, this can happen due to two reasons.

i. For websites that are recently migrated to new servers, it is possible that the email accounts might not be properly setup in the new server. This usually happens when migration was improper or incomplete due to connectivity issues in between.

When the customer in this migrated account tries to connect to the mail server using the old email username to send mails, the server would return an error as it cannot find a matching account.

At Bobcares, we ensure that such email errors do not occur, by validating the full list of email addresses during server migrations. Using a detailed migration checklist, we leave no stone unturned to ensure that every data is transferred during the migration.

ii. In cPanel servers, any auto-updates or scripts can cause the mail configuration files to have incorrect access permissions. This prevents the mail server from confirming the existence of a sender account, resulting in a 550 error.

Our expert engineers prevent such issues by validating the server functions and correcting the file and folder permissions post such updates and during our periodic server audit checks. There are scripts such as ‘mailperm’ that comes in handy for this.


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5 Comments

  1. Thanks for the helpful post. I was banging my head against the wall until I came across the “Duplicate sender account in recipient server”, which was the case after a site migration.

    Reply
  2. That’s great to hear. Thanks for the kind words! 🙂

    Reply
  3. Double check your cPanel settings under Authentication and ensure DKIM / SPF are disabled if you are using Mandrill.

    Reply
  4. I moved client CPanel over to a VPS hosting. Their domain just points to it via A Records, Mail is handled by an internal exchange for the whole building.. For some reason I still keep getting these emails, even though the CPanel doesn’t handle any mail? Was a real problem with WordPress too after migration, had to use sendgrid to send emails through the contact form. Do you have any thoughts on what this might be? Your solution only seems to address if the CPanel is also the mail exchange? Thanks a lot for your help in advance by the way Bob 🙂

    Reply

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