[plug] anti-spam + postfix

[Ben Jensz]

Hey all,

I'm looking at ways to try and close a loophole that is being used to 
still spam users on our mail server.

The problem is that the spammers are using the relay mail server 
operated by our ISP that is set to accept mail for our domain(s) (in 
case our mail server goes down) to relay spam through to us, hence 
evading maps_rbls rejections as the client delivering the mail to our 
mail server is our ISPs relay mail server and not the one that would get 
bounced by the maps_rbls rejections.

Any suggestions for overcoming this problem?  I have considered just 
removing the ISP relay server as a backup mx, but thats really not 
desirable or practical at all....

TIA for any suggestions.

Cheers,


Ben