Re: Spam filter

Either way, we have a dedicated FreeBSD mail server, and it's in to
stay. I got somebody off Windows. :)

I built a rather nice POP toaster with qmail (netqmail, not the broken
freebsd port) as the MTA, Courier IMAP for POP and IMAP, and sqwebmail
for web mail. It works pretty well, currently serving about a
thousand users but it could scale well beyond that. It's on a small
Shuttle XPC with a pair of ATA disks set up as a mirrored pair using
geom.

For spam control, I use greylisting (still amazingly effective against
bot spam), a small set of carefully chosen DNSBLs at SMTP time, then
spamassassin tagging the spam. I use a few simple procmail scripts to
look at the spamassassin results and put them into a subfolder.

I'm not entirely comfortable with all out blacklisting, so I haven't
enabled that firewall feature.

Some DNSBLs are a lot better than others. The Spamhaus lists have an
essentially zero error rate. The spamcop BL which used to have a lot
of misfires has greatly improved this year, so use that, too. If
you're willing to pay a modest amount of money (maybe $100/yr at your
volume) the MAPS/Trend RBL is pretty good, too.

b) You might want to consider farming the problem out to an e-mail
filtering service like: http://www.postini.com/

Outsourced filtering isn't a bad idea, but I would stay away from
Postini due to their infamously awful false positive problem and their
dreadful customer service. Messagelabs and MX Logic are far better.

R's,
John
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