I have seen increased amount of spam from the domains *.us, *.co.uk, *.asia, etc. Currently I am running a IMAP Based Mail Server with Spam Assassin doing the filtering. Its been doing great until now. Im trying to block everything from the above domains and everyday theres a new domain or two sending spam to the popular addresses on the mail server.
Whats the best way I can attack spam before it gets to the mail server? Having the mail server do the spam filtering is not helping anymore, so I would like to block / filter before it goes to the mail server and gets delivered to the users inbox.
Any help is appreciated. Preferably I would like a solution that works on Unix/Linux.