Could Not Complete Sender Verify (Sending Server)

Symptoms

1. When sending emails, in select instances, you can come across the following error message:

   CONFIG_TEXT: Could not complete sender verify

2. Or, if you've received a bounceback message, the errors can be:

   CONFIG_TEXT: Could not verify sender

   CONFIG_TEXT: Sender verify failed

   CONFIG_TEXT: 550: failed to verify sender'

3. Errors may vary in different email clients such as Outlook:

   CONFIG_TEXT: "email@domain.tld" is not a valid email address and has been rejected by the server. The message has been placed in your Outbox.

CPANEL_INFO: Please note, this article is for when the Sender Verify error happens on the sending server. If the error happens on the receiving server, please see this support article:

Could Not Complete Sender Verify (Receiving Server)

Cause

All of these errors essentially have the same meaning. One of the initial steps taken by the receiving mail server is processing a list of checks, one of which includes verifying that the receiving email account exists on the destination mail server to help avoid spam.

If the receiving mail server is unable to verify this, the email will fail delivery and generate one of the above error messages. However, oftentimes, the email account exists on the destination server, but other factors, such as network connectivity issues or duplicate entries of the domain within the server, can generate this error.

Resolution

1. Mail Routing for the destination and/or sending domains may be misconfigured. 
   The domain's mail routing should be set up where the mail servers are located. If the sending domain is not using external mail servers, it should be set to local. If the destination domain is not using the local mail server, then it should be set to remote. You can view details on how to change the mail routing for a domain here:

   How to change the MX or Mail Routing for a domain in WHM

2. Your server is unable to communicate with the destination mail server.

   At times, the server's resolvers can be unresponsive, causing external connections to fail. A quick way to check your server's resolvers to verify connectivity is to make use of the following internal cPanel script:

   # /scripts/check_unreliable_resolvers

    

3.  A typo in the destination email account.

   Copying and pasting an email account from another source and forgetting a character, in the beginning, is a common mistake. You'll want to ensure the email account is spelled out correctly.

   If the issue is still persistent after applying the above, then an additional review of the network interaction between the servers may be required.