"I run a Postfix-based mail server that services a few hundred users with an average load of a couple of thousand legitimate messages a day--but thanks to spam, the actual load on the server is much higher. I use Realtime Blackhole Lists (RBL) and Distributed Checksum Clearinghouse (DCC) clients on Postfix and SpamAssassin to reduce the impact of spam.
"RBLs are lists of IP addresses of known and potential spam originators. There are many RBL providers, such as Spamhaus, Spamcop, and DNSRBL. These lists are also known by various other names, such as blacklists or blocking lists. Mail servers can connect to RBL servers to check on IP addresses..."
