Re: [ietf-smtp] DSNs

Sam Varshavchik <mrsam@courier-mta.com> Wed, 06 May 2020 00:09 UTC

Return-Path: <mrsam@courier-mta.com>
X-Original-To: ietf-smtp@ietfa.amsl.com
Delivered-To: ietf-smtp@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 3B1733A0C6A for <ietf-smtp@ietfa.amsl.com>; Tue, 5 May 2020 17:09:51 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.9
X-Spam-Level:
X-Spam-Status: No, score=-1.9 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 6cLbcUhR2mVv for <ietf-smtp@ietfa.amsl.com>; Tue, 5 May 2020 17:09:50 -0700 (PDT)
Received: from mailx.courier-mta.com (mailx.courier-mta.com [68.166.206.83]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 0F5FA3A0C68 for <ietf-smtp@ietf.org>; Tue, 5 May 2020 17:09:49 -0700 (PDT)
Received: from monster.email-scan.com (monster.email-scan.com [::ffff:192.168.0.2]) (TLS: TLSv1.3,256bits,TLS_AES_256_GCM_SHA384) by www.courier-mta.com with UTF8ESMTPS id 00000000002A0091.000000005EB1FF20.0000673B; Tue, 05 May 2020 20:04:48 -0400
Received: from monster.email-scan.com (localhost [127.0.0.1]) (IDENT: uid 1004) by monster.email-scan.com with UTF8ESMTP id 000000000005E9B6.000000005EB1FF20.0000D275; Tue, 05 May 2020 20:04:48 -0400
References: <20200426203307.97DFB1863A8B@ary.qy> <cone.1587934924.981704.31890.1004@monster.email-scan.com> <20200505164840.GJ76674@straasha.imrryr.org>
Message-ID: <cone.1588723488.104539.34142.1004@monster.email-scan.com>
X-Mailer: http://www.courier-mta.org/cone/
From: Sam Varshavchik <mrsam@courier-mta.com>
To: ietf-smtp@ietf.org
Date: Tue, 05 May 2020 20:04:48 -0400
Mime-Version: 1.0
Content-Type: multipart/signed; boundary="=_monster.email-scan.com-34142-1588723488-0002"; micalg=pgp-sha1; protocol="application/pgp-signature"
Archived-At: <https://mailarchive.ietf.org/arch/msg/ietf-smtp/Csuc5LG4mMFXEWlwuYO2xYHHtuE>
Subject: Re: [ietf-smtp] DSNs
X-BeenThere: ietf-smtp@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Discussion of issues related to Simple Mail Transfer Protocol \(SMTP\) \[RFC 821, RFC 2821, RFC 5321\]" <ietf-smtp.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ietf-smtp>, <mailto:ietf-smtp-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ietf-smtp/>
List-Post: <mailto:ietf-smtp@ietf.org>
List-Help: <mailto:ietf-smtp-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ietf-smtp>, <mailto:ietf-smtp-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 06 May 2020 00:09:51 -0000

Viktor Dukhovni writes:

> The internal mailstore topology is none of the sender's concern, but
> also I do not wish to be a source of backscatter if the envelope sender
> address is fake.

Suppressing DSNs won't entirely prevent that. For whatever reason the  
internal mail server may end up bouncing it. The edge server, having  
accepted it and rewritten the recipient address has no guarantees that the  
rewritten recipient's address is deliverable. So it can still bounce and can  
generate backscatter.