On Dec 15, 2019, at 5:34 PM, Valdis Klētnieks
<valdis(_dot_)kletnieks(_at_)vt(_dot_)edu> wrote:
I admit not knowing how to express in RFC language the concept that the MTA
code MUST (2119 sense) allow address literals, while email admins be advised
that accepting them on the open Internet is, as a practical matter, somewhere
between MAY NOT and SHOULD NOT (but not rising to MUST NOT). In three
decades
of dealing with RFCs, I can't recall a prior instance where we've ended up
mandating that an implementation support something that's usually a bad
idea except in specialized corner cases...
Note that I've at no point advocated that receiving MTAs SHOULD NOT
(or MAY choose not to) accept address literals. They definitely
SHOULD accept address literals. I'm only saying that, despite the
foregoing, in practice they "may" (lower case) accept only FQDN forms,
and so a sending MTA is perhaps well advised to avoid their use.
That's why I let John Klensin write them. :)
Indeed. :-)
--
Viktor.
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