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From Sid Stuart <...@weaselworks.com>
Subject Re: preprocessing after smtp DATA
Date Sat, 19 Apr 2003 19:38:17 GMT
Serge Knystautas wrote:

> Hontvari Jozsef wrote:
>> It seems to me that the current james behaviour, accepting everything in
>> smtp, wonderfully attracts viruses, generating large and unnecessary
>> traffic. Rejecting most messages immediatly within the smtp session 
>> would
>> help.
> We've discussed the idea before, and some people have interest in 
> this.  I've been against it because of these reasons:
> 1. It makes mail processing synchronous instead of asynchronous, so 
> when you're mail server is busy, you become unable to accept both good 
> and bad messages.

I have a couple of concerns with this argument. First off, I've run 
several fairly large mail servers and have never seen connections 
blocked due to load. So in my experience you are raising a issue that 
does not occur in the majority of existing installations. The benefit of 
providing a customisable solution is that it lets the end user decide, 
based on their environment, whether the additional filtering is appropriate.

My second concern is the terminology is a little fuzzy. Saying "It makes 
mail processing synchronous..." makes it sound like the whole message 
processing function will be moved to the SMTP protocol sever. I don't 
think mail processing should occur at that level (and I don't think you 
do either). I do think a customizable mechanism should be available to 
validate remote hosts. If the host fails validation, then messages from 
it should be refused.

I have seen impressive results from the Exim connection filtering 
mechanism that tests to see if the initiating host has an STMP server on 
port 25. After moving from Sendmail to Exim, the spam level dropped 
80-90% at the sites I support. The level of spam dropped so much, I 
didn't even need to set up blackhole list filtering. (Alas, I no longer 
know where to buy Viagra to increase my breast size and reduce my 
mortgage payments.) While this kind of test could be put into the 
message processor, it does not naturally fit there.


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