FWIW I am religiously opposed to content-based filtering for exactly
this reason.
I "filter" only with blacklisting and greylisting. Although they
can only
be done at a boundary mail exchanger, I find it invaluable that
there's
really no such thing as a false positive; if legitimate mail
bounces then
it, well... bounces.
I do all kinds of crazy filtering. Some is content-based, although
recently I've been focusing on other criteria. Yes, there have been
occasional false-positives; when I find one, I fix it so it doesn't
happen again.
I do content-based filtering only after all other filtering options
have been exhausted. Messages with a sufficiently high score, I
don't bother looking at, and false positives there are nearly zero.
Messages with a questionable score, I do check periodically, so any
legitimate messages aren't lost, I simply don't see them as quickly
as I would if they weren't filtered. I find this situation much less
annoying than if I were to turn off content-based filtering altogether.
One thing I haven't set up yet is greylisting. It sounds very
effective, but I have some users that depend on being able to receive
an e-mail immediately (e.g. while they're on the phone with the
sender), and get quite annoyed when there's a significant delay. I
know, that's not how e-mail is supposed to work, but who am I to tell
them that? Still, I do want to do greylisting in certain cases; I
just haven't gotten around to setting it up yet.
Ugh, I hate spam.
~ Andy
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