Cannot "reject" email to non-existent user

[AdrianC]

Hello.

[Plesk panel 9.5.4 on CentOS]

I have a domain mysite.com and email [email protected]
I am going to domain > mysite.com > mail settings under "Mail to nonexistent user" I set "reject" and save.
Then I login to yahoo mail and send an email to [email protected] the server replies with failure notice

Remote host said: 550 sorry, no mailbox here by that name. (#5.7.17) [RCPT_TO]

I am expecting to silently reject the message sent to non-existent user. Or I got it wrong?
I tried fixing email settings with this command but there was no change: /usr/local/psa/admin/sbin/mchk

A spammer can hit any nonexistent email of my domain with a fake "from" address, then my stupid server replies to the fake "from" spamming him with the included message. This probably lists me as spammer :|

Thank you.

 

[ArnonW]

I believe that this is actually the correct behaviour for a mail server.
When an external client attempts to send email to a non-existent address, the mail server immediately replies with a "reject" status without accepting the message for processing. The bounceback email that you are receiving is not from the receiving host, but from the sending host notifying you that it was unable to deliver the message. Silently dropping such messages would be scary I think, so the sending host usually does this.
The receiving host never sends an outbound email, so it doesn't matter if the from address is fake.