"Recipient address rejected: User unknown in virtual mailbox table" when sending an email to just one address

Question

I have a server using Paralells 11.09 on a Centos 6 server, and my email account is hosted on there. About 2 weeks ago while emailing a client I received the following message from Evolution (my email client):

The reported error was "RCPT TO <[e-mail]> failed: <[e-mail]>: Recipient address rejected: User unknown in virtual mailbox table".

I thought it was an error with Evolution so I tried to send the email from my webmail account. But I received the same error when sending an email to that address.

I've tried sending emails to other accounts from the email account held on the server and they send fine and do not come up with this error. This error only occurs when I email this particular client from my email account on this server. If I send an email to his account from an alternative account held elsewhere I don't get this error.

What is going wrong?

Answer 1

RCPT TO failed: : Recipient address rejected: User unknown in virtual mailbox table

This error comes from Postfix attempting a local delivery of the message.

If it happens immediately when trying to send (as opposed to coming back later in a bounce message from a mailer-daemon), it would mean that your SMTP server "thinks" of itself as the final destination for the domain of your client. This is a misconfiguration if your client's mail is not hosted here.

On the other hand, when you send the mail from another account using another SMTP server, the mail is routed to the correct destination based on the DNS MX records of your client's domain.

Maybe the misconfiguration happened by entering your client's domain in Parallels for another purpose and it crept into the mail configuration as a mail domain.

A similar issue is answered here: Mail/Domain config issues - User Unknown in virtual mailbox.

Essentially it's about unchecking a box indicating that that domain's mail is handled by this Parallels instance.