I use SpamAssassin to filter spam out of my incoming mail, and it does its job admirably. I didn’t bother using DNS blacklists, since I didn’t really want to hand over control of what mail I accept to a third party, and was worried about false positives. However, with an average of about 3,000 spam mails per day getting shoved down to my home server for it to run spamassassin on, it was quite a waste of resources.
Recently I configured Postfix on my public-facing server to check against a couple of DNS blacklists – the most effective of which seems to be zen.spamhaus.org.
Here’s the number of spam mails which reached my home server each day:
[davidp@supernova:spam]$ grep -c '^From ' spam-2008-11-{27,28,29,30} spam-2008-12-*
spam-2008-11-27:3048
spam-2008-11-28:2759
spam-2008-11-29:3439
spam-2008-11-30:2853
spam-2008-12-01:3113
spam-2008-12-02:1231
spam-2008-12-03:155
spam-2008-12-04:193
spam-2008-12-05:78
spam-2008-12-06:92
spam-2008-12-07:61
See if you can guess which day the blacklisting was put in place :)
My guess would be the 2nd or 3rd.
Blacklisting really is an effective way to keep out the spammers. But have you lost any mails that you would prefer to have received?
Its really hard to figure out sometimes which are spammers and which are not..
So far, I’m not aware of any false positives!
Whats a false positive?