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Re: [ietf-smtp] CNAME considered harmful, was MTS-STS validation when MX host points to a CNAME

2021-04-04 12:01:05
No, and my apologies if parts of what follow sounds like a rant.

Thanks, I'd forgotten about the RFC 1123 language.

Once upon a time, we used to try to design protocols so that the
functionality that was needed was available but that the number
of different ways to do something was minimized, more or less on
the assumption that two or three ways to do the same thing
created opportunities for errors, ...

Yes indeed. In retrospect, CNAME was a mistake. If you look at RFC 1034, you can see that the motivation for CNAME was to provide short local versions of names and temporary forwarding when a host name changes. But now it's mostly used to transfer the management of a name to someone else.

The normal way to do that is with a zone cut, and I think that most applications of CNAME would better be done with NS. There are two differences: a zone cut needs to know what name is pointing at it and a zone cut covers all names below the redirected one while a CNAME doesn't, but in my experience, the situations where that matters generally have other problems.

Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly

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