Re: [ietf-smtp] MTS-STS validation when MX host points to a CNAME, violating RFC 2181 § 10.3

John Levine <johnl@taugh.com> Thu, 01 April 2021 00:30 UTC

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Date: 31 Mar 2021 20:30:22 -0400
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From: "John Levine" <johnl@taugh.com>
To: ietf-smtp@ietf.org
Cc: marka@isc.org
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Subject: Re: [ietf-smtp] =?utf-8?q?MTS-STS_validation_when_MX_host_points_to_?= =?utf-8?q?a_CNAME=2C_violating__RFC_2181_=C2=A7_10=2E3?=
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It appears that Mark Andrews  <marka@isc.org> said:
>You need properly read the quoted section that talks about MX target being a CNAME.
>In particular this sentence from RFC 5321, section 5.1:
>
>   Any other response, specifically including a value that will return a
>   CNAME record when queried, lies outside the scope of this Standard.
>
>In other words “It is your problem if the target of the MX refers to a CNAME
>and things break."
>
>The MX records for n0.lt are NOT RFC compliant.  The target points to a CNAME.

Quite right.

"Doctor, doctor, it hurts when I do this."

"So don't do that."

R's,
John