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Re: [ietf-smtp] Who should set the Sender: header field?

2021-12-17 06:19:25
On Fri 17/Dec/2021 04:10:43 +0100 John C Klensin wrote:
--On Thursday, December 16, 2021 21:30 -0500 John R Levine wrote:
On Thu, 16 Dec 2021, John C Klensin wrote:
When that new way of doing things will break the multiple From
option, mess up mailing lists (although people are welcome to
use their various group and social network services instead),

I'm with you on mailing lists, but the support for multiple
From is spotty even outside of gorilla land.

I'm not sure what to say about it but we are doing people no
favors by suggesting that mail with multiple from address is
likely to work.

I would favor a statement in the proposed A/S about this (or any
similar feature) warning people that the feature is not widely
supported, that it cannot be expected to work universally in an
interoperable way, may result in mail being bounced and/or lost,
and hence should probably be avoided unless the sender knows it
will be handled properly at the recipient end.  I'd be hesitant
about removing the construction from 5322bis entirely, but could
be convinced.

The _only_ thing I would object to is arguing that the standard
must be changed because one or several perceived large Gorillas
have decided to not support it.

Since G say they banned multi-mailbox From: after DMARC (with no statement about how/if it worked before), perhaps if we rewrite DMARC so as to not preclude the authentication of that kind of messages, they might eventually restore the functionality. Authenticating the sender of a multi-mailbox From: message does not suggest that its end-to-end flow is likely to work, but neither denies it.


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