Other Trick For Blocking Spam

This section is for other tricks to block spam that may or may not directly relate to SpamAssassin.

Fake MX Records

Email is supposed to be sent to the lowest numbered MX record first with the higher MX records being backup servers. Spammers often with try the highest MX record first thinking that the backup servers have less spam filtering than the main email server. They try the highest MX record and then never come back. So I set my highest MX record to point to an IP address that always returns a temporary "Come Back Later" error.

A real email will retry and get through. But the spammer will just go away. This trick saves having to process about 25,000 messages a day on my server.

Long delay (high latency)

I've seen that after changing my mail system from an old 486 with a very slow Internet connection (about 80 ms) to a fast server with just 5 to 10 ms, I got much much more spammail. Obviously spammers don't have much time to deliver one single mail. So it might help for a server which receives just some mails a day (maybe less than 200 a day) to increment the delay. I've seen no way to do this with iptables or ipfilter but maybe someone has an idea for this.

Rolf Winterscheidt