UIDS are more than simple 'message numbers'; they are part of a tuple (Folder, UIDVALIDITY, UID). It may be easy to think of UIDVALIDITY as a kind of 'generation number': for a given folder, as long as the UIDVALIDITY has not changed/incremented, the UID-to-messege has to be the same per the spec.
Though recently the OBJECTID extension has been published:
* https://tools.ietf.org/html/rfc3501#section-2.3.2
UIDS are more than simple 'message numbers'; they are part of a tuple (Folder, UIDVALIDITY, UID). It may be easy to think of UIDVALIDITY as a kind of 'generation number': for a given folder, as long as the UIDVALIDITY has not changed/incremented, the UID-to-messege has to be the same per the spec.
Though recently the OBJECTID extension has been published:
* https://tools.ietf.org/html/rfc8474