Can pf block illegal relay access attempts?

[Ladislav Bodnar]

Hi,

Over the last 7 days my Postfix mail server received almost 80,000 requests 
to relay mail to a third destination. Since it is not an open relay, it 
rejected all these requests, but it is still annoying to see this 
happening. The requests came from varying (almost 20,000 different) IP 
addresses, but they had one thing in common - the destination address was 
always "$some-user-name"@infomagic.com.

Is there a way to prevent these attempts to access the mail server at all? I 
only started using pf recently, so I still have a lot to learn, but I would 
appreciate any advice. Or is pf not the right tool for this?

Thanks a lot for your help.