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.

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.

2. Duplicate sender account in recipient server

Another issue we’ve seen related to migration is that users cannot send mail from a recently migrated domain to domains hosted in the previous server (server from which the domain was migrated).

This happens when the migrated domain was not properly removed from the source server. If the sender email address accidentally exists in the recipient’s mail server, then this recipient server can reject the mail with the error ‘550 Sender verify failed’.

For instance, domain1.com was recently migrated from server1 to server2. Now domain1.com cannot send mails to domain2.com which is hosted in server1, if server1 still has the mail accounts for domain1.com.

Email rejection happens because the recipient server is unable to lookup the correct sender domain, due to its local mail entries, causing it to consider it as a spam attempt and bounce the mail.

When Bobcares handles account migrations, we avoid such issues by performing a post-migration check to prevent such phantom accounts and left overs in the source server.

Using a detailed checklist, our website technicians validate the transfer done, including email accounts, filters and the databases. After confirming that the domain is fully functional in the new server, we remove its traces from the old one to avoid any errors.

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3. Misconfigured mail exchanger

Some domains use external mail servers like Google Apps for their email purposes. For using external mail servers, the email settings of these domains should be updated for remote delivery instead of local.

We’ve seen many instances where the site owners did not enable such remote MX routing for such domains, causing the emails to route incorrectly and bounce back with the error ‘550 Sender verify failed’.

To check this possibility, we audit the MX records of the domain, and if it is not pointing to our server, we reconfigure the ‘Email Routing’ for this domain using “Remote Mail Exchanger”.

Another setting that can lead to ‘550 Sender verify failed’ is the ‘sender callout verification’ feature. Inorder to combat spam, the recipient server accept mails from a sender only after connecting back to it and verifying that the sender is valid.

From our experience, we’ve seen that this callout feature can create a lot of overhead and can lead to email bounces. We resolve such issues by bypassing the sender mail server or by disabling this feature, depending on the impact of the error.

In short..

Though email errors can lead to disruption of normal business functionality, we’ve been able to prevent majority of such errors with proper planning and timely proactive checks of website functions.

Bobcares’ website support specialists perform all website management tasks such as hack recovery, website migration, CMS upgrades, database restores, and error fixing. If you’d like to know how to make your site the best, we’d be happy to talk to you.