This not an answer to your question, but I was going to ask for the same referrals. I've been
searching for one the last couple of days. There
are companies that will filter out your mail for
you ie; mail-abuse.com, messagelabs.com... but not sure on the cost for this service.
I will be contacting these vendors tomorrow as I
also think that my legacy Netscape Messaging Server 4.15 have been hijacked despite of the
anti-relay and mail filtering in place.
It seems the spammers have out-smarted this server.
I will be posting for help on this mail server that I have.
In the meantime, I'm looking for alternatives to help fight these spammers. I let you know the cost of the services I mentioned.
Good Luck
Trc