I have an email server Postfix (not open relay) filtered with ASSP (filter incoming mail/connection), but some spammer is sending tons of spam using my email server by using fake local address.
This fake local address makes it seems that the email come from users of my email server.
He can't use his (from) email address, I already put some filter (multiple instance postfix).
The fact that he send the email using fake local address (randomly generated), makes it hard to fight.
I've fix (but not totally) the problem using postfix check_sender_access (list all local sender), but seems not that effective.