> In article <7877.1502972732@xxxxxxxxxxxxxxxxxxx> you write: > >This is an interesting idea. For those of us who deal with many emails, > >(particularly upon return from vacation), not having to deal with lunch plans > >that have expired would in fact be nice. > See RFC 2156 and RFC 4021, section 2.1.50. To me the interesting > question is why, since we've had Expires: for 20 years, nobody uses it > outside of netnews. More like 30+ years. See RFC 841, section 3.2.5, also X.400-1984. > > That's a job for good-old-Usenet Supersedes:, > >but that's one email overcoming another, and the whole thing needs > >some cryptographic support. Note that a merkle hash (a la s/key) would > >probably suffice. > Seems like overkill. How about you pay attention to the Supersedes: > (see RFC 2156 and RFC 4021, section 2.1.46) if old and new messages > both have DKIM signatures from the same domain? Same question about > why after 20 years nobody uses it outside of netnews. And if you want to explore the cryprographic side of this, there's an extensive literature. A good place to start is Radia Perlman's "The Ephemerizer - Making Data Disappear". Ned