Nov. 7, 2017
12:53 a.m.
On Mon, 6 Nov 2017, Mark Svancarek wrote:
Clarifying, since this question comes up from time to time:
Also note that only the initial sender can do this. If mail goes A->B->C, A can downgrade if the A->B hop can't do EAI, but B cannot if B->C can't
Is this a MUST or a SHOULD (recognizing that RFC-style SHOULD is still very firm)?
MUST, absolutely, not negotiable. B does not know what addresses A considers to be equivalent. To clarify, we're talking about forwarders, not mailing lists. Lists conceptually originate a new message (even if it looks a lot like the incoming message) and do all sorts of funky stuff to messages on the way through. Regards, John Levine, john.levine@standcore.com Standcore LLC