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kashani wrote: |
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> 1. Block mail up front. |
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> Use greylisting as it stops spam before it enters the MTA's queue. |
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> This keeps 90% of my spam from even entering the more resounce |
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> intensive filtering processes. |
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> |
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This is a very effective filter. However, it does greatly slow down |
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delivery of legitimate email. I found it a bit of a pain. Further, |
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there are those servers out there that respond to greylisting as a |
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bounce, so you need to specifically configure accordingly. |
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> 2. Don't use blacklists |
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> 30% false positive rate. Comapared to 1-2% for Bayesian or |
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> Markovian filtering. |
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> |
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I use both. As far as false positive goes, I have had very few false |
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positives ... in fact, i can not think of any. But, for a corporate |
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setting, I would not use it, but instead leave it all to software like |
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DSPAM or Spam Assassin. |
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> 3. Do some simple check up front, but don't do too many. |
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> Require a helo, reject invalid hostnames, reject unknown domains, |
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> reject non FQDN, and that's pretty much it. Requiring DNS to match and |
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> other checks is something you can do, but I've found that there are |
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> too many poorly configured legitimate mail servers for this to be |
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> worth the hassle. |
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> |
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All corporate servers should implement this IMHO ... |
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I am always surprised how many sites out there send mail directly from |
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webservers in a DMZ that do not have proper FQDN setup. I tend to find |
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these upon making an order and not getting an email ... log searches |
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reveal the problem. So, if you want maximum ability to receive email, |
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don't enforce these rules. |
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|
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Tom Veldhouse |
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-- |
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