> I use check_sender_access and DISCARD to throw away about 1500-4000
> messages a day from .top domains (which is about the volume of my
> legit email). I looked into it and most of them are registered
> to namecheap.com, which appears to sell the names for for $.98
> each. I did a little research into Namecheap's reputation and I
> found one thread calling them friendly to spammers.
If you have reasons to believe that a certain DNS server is hosting
spammer domains, you can use check_client_ns_access, check_helo_ns_access
and check_sender_ns_access to block present future spam.
It helped me to block a persistent spammer who was constantly changing
domain names, but who kept using the same DNS server.