Re: [ietf-smtp] Should we update an RFC if people refuse to implement parts of it ?

Alessandro Vesely <> Tue, 01 June 2021 17:32 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id C12193A212A for <>; Tue, 1 Jun 2021 10:32:33 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.799
X-Spam-Status: No, score=-2.799 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (1152-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id eR3v6CrigJZP for <>; Tue, 1 Jun 2021 10:32:28 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 3EEF93A2127 for <>; Tue, 1 Jun 2021 10:32:27 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=delta; t=1622568743; bh=eX6DWFiv5Nr+LhKpnDls/I1j1iWeYO5lY6C5PDNrM5k=; l=2295; h=To:References:From:Date:In-Reply-To; b=BG+XtZF7EzN7tpyorA6ZKq6i3mSm9hZtasI0F6q5ntCby1kzBdaLskmOTS/FixfBN f0iJjyqgJnZmBur7243CUYYRK4/5ezfSb6CEtwm4TRd8uXKyTPHWC8cOlTq0LMicw8 aPbza36LQgEqIYpTOmqXXjpXBlb70yZZw07MGTONArqCwqfd93lY2i8SGwB2F
Authentication-Results:; auth=pass (details omitted)
Original-From: Alessandro Vesely <>
Received: from [] (pcale.tana []) (AUTH: CRAM-MD5 uXDGrn@SYT0/k, TLS: TLS1.3, 128bits, ECDHE_RSA_AES_128_GCM_SHA256) by with ESMTPSA id 00000000005DC0CB.0000000060B66F27.00007E1F; Tue, 01 Jun 2021 19:32:23 +0200
References: <20210525182946.079748B872C@ary.qy> <EFDA46E00EFF0E48802D046A@PSB> <> <> <> <E23639ADA7487360C9B5A93C@PSB> <>
From: Alessandro Vesely <>
Message-ID: <>
Date: Tue, 1 Jun 2021 19:32:22 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0
MIME-Version: 1.0
In-Reply-To: <>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Archived-At: <>
Subject: Re: [ietf-smtp] Should we update an RFC if people refuse to implement parts of it ?
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Discussion of issues related to Simple Mail Transfer Protocol \(SMTP\) \[RFC 821, RFC 2821, RFC 5321\]" <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Tue, 01 Jun 2021 17:32:34 -0000

On Tue 01/Jun/2021 02:54:32 +0200 Ned Freed wrote:
> To the extent Received: fields are relevant to our customers, it's to track down
> the cause of some sort of problem, usually but not always some kind of delivery
> delay. I find A-label better suited to this usage than U-labels.

Nowadays, Received: fields are often intermixed with Authentication-Results:, especially near the top of the header.  The latter provides U-Labels, AFAICS.  That way, both kinds of labels are available.  Here's a couple of examples:

By Courier-MTA:

Return-Path: <>
   spf=pass smtp.mailfrom=foà.it;
   dkim=pass (whitelisted) header.d=foà.it
Received: from ( [])
   by with ESMTP
   id 00000000005DC026.0000000060B66AC3.00007C42; Tue, 01 Jun 2021 19:13:02 +0200

By Google:

        dkim=pass header.i=@foà.it header.s=gamma header.b=BHORghd0;
        spf=pass ( domain of postmaster@foà.it designates as permitted sender) smtp.mailfrom=postmaster@foà.it;
        dmarc=pass (p=NONE sp=NONE dis=NONE)

Still, Section 3.7.3 of RFC 6531 doesn't seem to say that A-R's are trace fields...

>> On the other hand, and here comes the question: There are proposals
>> floating around that would define new header fields that would
>> reflect, include, or depend on, different sorts of forward-pointing
>> and reverse-pointing addresses.  Should we be taking the position
>> that none of those should move forward unless they explicitly
>> address what should be done when those fields are not traditional
>> ASCII ones?> 
> Very good point. EAI is a standards-track format/protocol. An unavoidable
> consequence of this is that proposal that involves a new header field needs to
> say how it interacts with EAI, even if it's only to say it doesn't interact at
> all.

If not specified, it looks like Section 3.6 of RFC 6532 supplies a default:

    encoded-words SHOULD NOT be used when generating header fields for
    messages employing this extension.  Agents MAY, when incorporating
    material from another message, convert encoded-word use to direct use
    of UTF-8.