I believe that if you don't return UIDVALIDITY, it means that the server doesn't support persistent UID's. UIDs are still supported, but they won't persist from one select to another.
No, UIDVALIDITY is required from an IMAP4 and IMAP4rev1 server.
If UIDs are not persistent, then UIDVALIDITY is returned as a session-specific value which is undefined but is greater than the value returned from a previous session. The 32-bit UNIX format date/time of SELECT time is a good value to use for this.
Note that since UIDVALIDITY is unsigned, this doesn't need to be fixed in 2038 but can wait until 2106. Since I fully intend to be dead in 2106 (I'd be 150 years old otherwise) I'm not going to worry about how to fix it... :-)
-- Mark --
http://staff.washington.edu/mrc Science does not emerge from voting, party politics, or public debate. Si vis pacem, para bellum.
