Load Balancing with Postfix [and SpamAssassin]

Lonnie Olson fungus at aros.net
Thu Jan 19 11:29:46 MST 2006


Michael Torrie wrote:
> On Wed, 2006-01-18 at 15:25 -0700, Tyler Strickland wrote:
> 
>> Have you considered switching antispam software?  When I was looking into
>> antispam software last year, I seem to remember seeing that other
>> packages, like DSPAM, used far fewer resources than SpamAssassin.

SA doesn't do too well with a default config.  However with just a 
little bit of tweaking SA can be *very* effective.  SA does much much 
more than just bayesian filtering and DNS blacklists.  It can also score 
via Razor[1], Pyzor[2], and even DCC[3].  When combined SA beats out 
dspam any day.  Yes it becomes a resource hog, but that is where the 
cost of good filtering comes in.

> 
> Also, consider gray-listing  (sqlgrey comes to mind).  This should
> reduce the amount of spam actually getting delivered (spam just won't
> get through most of the time!) and having to go through spamassassin.
> I'm about to implement this at work and try it for a while.

Greylisting is an amazing idea and will reduce the amount of spam that 
even gets to SA by a great deal.  However, using it for business mail or 
for mail that that is delivered to your customers (eg. ISP).  It just 
isn't feasible.

Imagine a business client of yours needs to send you an email right 
away.  Up until now your only contact has been via phone.  Now this 
email will need to be responded to right away.  He sends it.  Your 
server is now going to refuse it for a few hours.  After that, assuming 
his mail server is configured to keep trying past those few hours, you 
get the email, but look very bad to your client.

Another problem is that of misconfigured servers.  I have run into some 
that the retry schedule increases dramatically, this can cause mail to 
be delayed a very long time.

Basically, for your personal email it is a great way to reduce spam, but 
keep that whitelist current.

--lonnie
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