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[ietf-smtp] smtp extension model (was: Re: [Proposal] confusing parts of the mail system, was 250-MARKDOWN)

2019-01-30 13:39:12
On Thu, Jan 17, 2019 at 5:41 AM Ned Freed 
<ned(_dot_)freed(_at_)mrochek(_dot_)com> wrote:

On 17/01/2019 04.29, Ned Freed wrote:

Clearly not, as you yourself have noted.

Microsoft supports BINARYMIME for received mail on port 25.

This something that, I hear, is very difficult for others to do.  I'm
told it's very complicated.  Somehow they have figured out how to make
this work.

They have not figured out how to make it work, because it's not possible to
make it work in general. Transcoding destroys DKIM signatures, period. So

(1) Reject messages sent with BINARYMIME and signatures, either in all
    or in cases where they know they are going to forward, leading to
    unncessary failures, or,

(2) Accept such messages and trash the signatures, leading to unnecessary
     failures, and,

(3) Deal with dynamic forwarding cases either by not having any or
    falling back to (1) or (2), leading to unnecessary failures.

Would it be useful to write an informational rfc "The SMTP Extensions Model
in 2019" to discuss these pitfalls in detail? 5321 2.2 doesn't have a lot
to say about what to do in this case.

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