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Re: [Uta] Eric Rescorla's Discuss on draft-ietf-uta-smtp-require-tls-07: (with DISCUSS and COMMENT)

Eric Rescorla <ekr@rtfm.com> Thu, 14 March 2019 17:32 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Thu, 14 Mar 2019 10:31:32 -0700
Message-ID: <CABcZeBMPgm1yG0K513D9WsytS9Y+=cH38SnKcHkveqSrsUcpkQ@mail.gmail.com>
To: Nico Williams <nico@cryptonector.com>
Cc: uta@ietf.org, uta-chairs@ietf.org, draft-ietf-uta-smtp-require-tls@ietf.org, The IESG <iesg@ietf.org>
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Subject: Re: [Uta] Eric Rescorla's Discuss on draft-ietf-uta-smtp-require-tls-07: (with DISCUSS and COMMENT)
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On Thu, Mar 14, 2019 at 10:27 AM Nico Williams <nico@cryptonector.com>
wrote:

>   | 4.  Policy Validation
>   |
>   |    When sending to an MX at a domain for which the sender has a valid
>   |    and non-expired MTA-STS Policy, a Sending MTA honoring MTA-STS MUST
>                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>                                                      ^^^^^^^^
>   |    check whether:
>   |
>   |    [...]
>   |
>   | 5.  Policy Application
>   |
>   |    When sending to an MX at a domain for which the sender has a valid,
>   |    non-expired MTA-STS Policy, a Sending MTA honoring MTA-STS applies
>                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>                                                  ^^^^^^^^
>   |    the result of a policy validation failure in one of two ways,
>   |    depending on the value of the policy "mode" field:
>   |
>   |    [...]
>
> How does this not allow a sending MTA to... not honor MTA-STS?
>

It's allowed to not *generally* honor STS, but this text does not have any
provision for just ignoring it for some messages. Any other reading seems
extremely strained.

-Ekr


> Nico
> --
>

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