[please do not Cc' me, thanks]
> The important sentence in that is: "The dialog is purposely lock-step". So
> 2821 is slightly self-contradictory, this is not news. (note that the command
> in question is an effective null command of connection opening).
This is only "slightly self-contradictory" if you consider connection
opening "an effective null command" which is certainly an unusual
interpretation and IMHO not covered by RFC 2821.
BTW: please bring those "slightly self-contradictory" items up
on ietf-smtp when RFC2821bis will be published (probably next week).
If there's anything unclear in RFC2821(bis) then now is the chance
to fix it.
> If you see violations of SHOULDs, it's also always worth asking what the
> good reason is.
I'm not questioning that. It's maybe just a bit "nit picking":
the error message is misleading as it is not a _violation_ of RFC 2821.