On Tue, 29 Nov 2022, John C Klensin wrote:
Pretending (accidentally or intentionally) that the MIXER definition and the X.400 definition on which it depends and that any other implementations have the similar (see below) semantics are the only use to which "Expires:" has been put historically is just not realistic.
The only Expires: headers I have ever seen in e-mail are ones that came through usenet gateways. On usenet, it's fairly common to use an Expires: header in status or announcement messages sent on a schedule. Usenet hosts have a shared message spool that all of a host's users see, and Expires is a hint (not command) about when to delete the message from the spool which has a side effect that people can't see it any more. I think that is compatible with our usage.
What else has this header meant? And if it's meant something other than what MIXER said, how could you tell which is a MIXER header and which is whatever else it might have been?
I note in passing that if this is a real problem, which I do not believe it is, an MDA or MUA can easily look at the date on a message and if it's before 2022, the Expires header is not one of ours.
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
