SMTP Error 550, Recipient address rejected

An Email was sent to by, and Error message “SMTP Error (550): Failed to add recipient …: Recipient address rejected: User unknown in virtual mailbox table)” is shown. 

But the email is correct. Finally it is found that both domins are in the server. And HansaPlus Mail server is applied in addtional mail server. In the server there is Postfix mail server, and Postfix mail server always tries to deliver an email locally first. As exists on a local server, Postfix looks for a locally without checking the domain’s external mail service. Of course, is unknown to the server.

In order to resolve the issue, mail service for the recipient domain in the server should be disable.  

  1. In Plesk, go to Domains > > Mail Settings.
  2. Disable the option Activate mail service on this domain

After is is deactivated, the email can be sent successfully.

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