Re: [Emailcore] Ticket #5: G.5. Remove or deprecate the work-around from code 552 to 452?

Todd Herr <todd.herr@valimail.com> Mon, 08 March 2021 21:40 UTC

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From: Todd Herr <todd.herr@valimail.com>
Date: Mon, 08 Mar 2021 16:40:19 -0500
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Subject: Re: [Emailcore] Ticket #5: G.5. Remove or deprecate the work-around from code 552 to 452?
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On Tue, Feb 16, 2021 at 8:19 AM Todd Herr <todd.herr@valimail.com> wrote:

> On Mon, Feb 15, 2021 at 8:42 AM Alexey Melnikov <aamelnikov@fastmail.fm>
> wrote:
>
>> Hi,
>>
>> On Tue, Jan 19, 2021, at 4:24 PM, Alexey Melnikov wrote:
>> > Hi all,
>> >
>> > The first pagaraph of Section 4.5.3.1.10 (Too Many Recipients Code)
>> > currently says:
>> >
>> >     RFC 821 [3] incorrectly listed the error where an SMTP server
>> >     exhausts its implementation limit on the number of RCPT commands
>> >     ("too many recipients") as having reply code 552.  The correct reply
>> >     code for this condition is 452.  Clients SHOULD treat a 552 code in
>> >     this case as a temporary, rather than permanent, failure so the
>> logic
>> >     below works.
>> >
>> > John noted that this suggestion may have outlived its usefulness
>> > and/or be inconsistent with current practice. Should it be removed
>> > and/or explicitly deprecated?
>>
>> I did a bit of digging and it doesn't look like Sendmail emits 552 or
>> treats it as 442 if received from other MTA.
>> Postfix code has this commented out with a note that this workaround
>> creates more problems than it solves, due to other meaning of 552.
>>
>> Do people have information about other MTAs (not necessarily open source)
>> on this topic?
>>
>>
> I've reached out to a few large mailbox providers and a couple of
> commercial MTA vendors on this question. Still collecting answers, but hope
> to post results here by the end of the week.
>

Long delayed and incomplete results from an informal survey of a few
providers and commercial MTA vendors (all of whom I've suggested should
make their presence known here..)

Google: Emits 452, treats 552 as permanent failure
Microsoft: Emits 550, treats 552 as permanent failure (probably)
Proofpoint MTA: No default configuration for too many recipients, so emits
whatever admin wants; treats 552 as permanent failure.

If I receive any more information, I'll post it.

-- 

*Todd Herr* | Sr. Technical Program Manager
*e:* todd.herr@valimail.com
*m:* 703.220.4153

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