(1) The X.400 definition, and hence the MIXER one, is a little vague about the actual meaning of "loss of validity" and any terms that are used instead of it.
I suppose, but after 25 years, I don't think anything else we said would make any difference. "Expires" has an English meaning, it's fairly obvious how it would apply to a mail message, and people will do something that makes sense to them for expired messages regardless of how many MUST or MUST NOT we might add, trying to guess what they might do that we might not approve of.
The goal here is to interoperate, and we've squeezed all the interop advice blood from this turnip that there is to be squeezed.
Regards, John Levine, johnl@xxxxxxxxx, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. https://jl.ly -- last-call mailing list last-call@xxxxxxxx https://www.ietf.org/mailman/listinfo/last-call
