An Email was sent to email@example.com by firstname.lastname@example.org, 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 hansaplus.com exists on a local server, Postfix looks for a email@example.com locally without checking the domain’s external mail service. Of course, firstname.lastname@example.org is unknown to the server.
In order to resolve the issue, mail service for the recipient domain in the server should be disable.
- In Plesk, go to Domains > mydomain.com > Mail Settings.
- Disable the option Activate mail service on this domain
After is is deactivated, the email can be sent successfully.