postfix-users October 2010 archive
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postfix-users: RE: Fighting Backscatter

RE: Fighting Backscatter

From: Terry Gilsenan <terry.gilsenan_at_nospam>
Date: Wed Oct 20 2010 - 01:27:29 GMT
To: Steve Jenkins <steve@stevejenkins.com>, Postfix users <postfix-users@postfix.org>

From: owner-postfix-users@postfix.org [owner-postfix-users@postfix.org] On Behalf Of Steve Jenkins [steve@stevejenkins.com]
Sent: Wednesday, 20 October 2010 10:52 AM
To: Postfix users
Subject: RE: Fighting Backscatter

>I will gladly solve the RIGHT problem. The fact that I'm here looking for
>guidance should demonstrate that I'm looking to do exactly that.
>Unfortunately, I can't simply put "DO NOT forward SPAM" in my main.cf and
>have it work. ;) After reading through all the docs and various blog and
>forum posts, and making my best efforts at incorporating what I've learned
>into my configuration, it seems I'm still causing backscatter. That's
>exactly why I'm posting on Postfix-users - because I need a little more
>guidance than just "RTFM." :) So if anyone can help me with some SPECIFIC
>steps to take, I'd be very appreciative.

Steve, Backscatter is caused by a configuration that accepts all email and then bounces email it cannot deliver. This is where your configuration is faulty.

Only accept email that you can deliver! If you cannot deliver email for any reason you should be determining this within the SMTP transaction phase and responding to the sending MTA with the appropriate rejection code.

Any email that you do actually accept and for which your server tells the sending MTA "OK", you either need to deliver or if your filters are setup appropriately, quietly sink. (purists will say this should never happen, but pragmatists reallize that some content inspection testing cannot be done until the email has been fully rec'd)

If you have this sorted out then your backscatter problems will go away.

Rule of thumb: Start with a config that accepts nothing, then add exceptions for things that you want to accept email for, and nothing else.