[Exim] Blocking incessant relay testers with Exim 4

As any MTA operator will quickly notice, relay testing by spammers is a
common occurrence. Worse, many of the idiots doing the testing ignore the
"Relay not permitted" and carry on testing, over and over again.

I'd like to deny SMTP connections to certain hosts and IP blocks, and was
wondering what is the best way of doing it with Exim 4. I can do it quite
easily with an ACL on the router, but would prefer to maintain a file with
host IP address and ranges for the MTA instead.

Thought host_reject_connection would be the way to go, initially, but
the Spec says it's better to reject at a later stage. What's the reasoning
for this?



--
Juha Saarinen