421 4.3.0 deliver: Trying to unput wrong character

[Merlin Hartley]

Hi Mikhail

This is one of those weird inconsistencies between IMAP and SMTP protocols … as far as I remember, the NUL character restriction only applies to the IMAP protocol … so your MTA (e.g. sendmail) is not breaking the SMTP RFC by transferring them.
In my Exim configuration I have some code which strips the NUL characters from externally received messages and prohibits my local users from submitting messages which contain them - you could probably come-up with a similar thing for sendmail.
This may be useful: http://info-cyrus.andrew.cmu.narkive.com/Rro4Nn9M/554-message-contains-nul-characters

Merlin
--
Merlin Hartley
Computer Officer
MRC Mitochondrial Biology Unit
Cambridge, CB2 0XY
United Kingdom

> On 24 Jul 2017, at 17:14, Mikhail T. <mi+cyrus at aldan.algebra.com> wrote:
> 
> On 24.07.2017 10:41, Merlin Hartley wrote:
>> NUL characters are not permitted in e-mails … 
>> https://helpdesk.pscs.co.uk/690163-Data-stream-contained-NUL-character <https://helpdesk.pscs.co.uk/690163-Data-stream-contained-NUL-character>
>> 
>> As the RFC for IMAP states:
>> https://tools.ietf.org/html/rfc3501#section-9 <https://tools.ietf.org/html/rfc3501#section-9>
>> (3) The ASCII NUL character, %x00, MUST NOT be used at any time.
> But the message did go through sendmail...
> 
> Ken Murchison wrote:
>> What is the Content-Transfer-Encoding of the email? Was the message Base64 encoded, or is the PNG included as raw binary data?
> Raw... Here are the full headers (the first line -- the From_ -- is removed by sed before feeding the rest into deliver):
> From mi at EXAMPLE.com <mailto:mi at EXAMPLE.com>  Mon Jul 24 00:53:00 2017
> Received: from narawntapu.narawntapu (localhost [127.0.0.1])
>         by narawntapu.narawntapu (8.15.2/8.15.2) with ESMTPS id v6O4r05T003160
>         (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO)
>         for <mi at narawntapu.narawntapu> <mailto:mi at narawntapu.narawntapu>; Mon, 24 Jul 2017 00:53:00 -0400 (EDT)
>         (envelope-from mi at narawntapu.narawntapu <mailto:mi at narawntapu.narawntapu>)
> Received: (from mi at localhost)
>         by narawntapu.narawntapu (8.15.2/8.15.2/Submit) id v6O4r0c9003159;
>         Mon, 24 Jul 2017 00:53:00 -0400 (EDT)
>         (envelope-from mi)
> Date: Mon, 24 Jul 2017 00:53:00 -0400 (EDT)
> Message-Id: <201707240453.v6O4r0c9003159 at narawntapu.narawntapu> <mailto:201707240453.v6O4r0c9003159 at narawntapu.narawntapu>
> From: Cron Daemon <mi at EXAMPLE.com> <mailto:mi at EXAMPLE.com>
> To: mi at narawntapu.narawntapu <mailto:mi at narawntapu.narawntapu>
> Mime-Version: 1.0
> Content-Type: image/png; charset=binary
> Content-Transfer-Encoding: 8bit
> Subject: Cron <mi at narawntapu> cat foo.png
> Should sendmail have re-encoded with something other than 8bit? I don't like doing that, because it increases the filesizes to no obvious benefit... Thanks!
> -mi

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