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Re: Initial Installation Step 2

From: Andrew Daviel
Subject: Re: Initial Installation Step 2
Date: Thu, 25 Jun 2009 16:59:47 -0700 (PDT)

On Thu, 25 Jun 2009, Don Armstrong wrote:

[Though in reality, you should really just discard spam messages
instead of rejecting them.]

The whole point of a milter IMO is that you can reject suspicious mail without your MTA generating a message back to a probably bogus return address.

If the mail is genuine, but the sender has done something like send a big attachment with no content, or sent a virus sample, then their MTA sends then a nondelivery message which includes the text string from the error status. If they actually read it (unlikely), it will tell them why their mail was not delivered.

If the mail is sent from a direct-to-MX botnet, chances are the agent ignores the error status entirely. (Having the address flagged as undeliverable would be too much to hope for).

On the other hand, giving success status to all mail might encourage SMTP scanners to think the address is valid and add it to mailing lists.

Andrew Daviel, TRIUMF, Canada
Tel. +1 (604) 222-7376  (Pacific Time)
Network Security Manager

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