In all my systems I have the hostname and the mail domain. So say mailserver.domain.it and the mail domain is domain.it. Nothing special.

But in most of my installs the systema mails (mail sent from CLI with the mailx command) have the @mailserver.domain.it domain, which often doesn't exist, or is certainly not a mail domain.

Other than that, my virus / spam notifications are generated and sent to the mailserver.domain.it domain! And this IS a problem because they're sent to an unexisting address.

Any idea why this happens? How to fix?