>Message-ID is not unique per message

Thank you for saving me from the heartbreak of finding this out later. Seriously you just saved me a ton of time.

>A UIDVALIDITY change should blow your whole cache. In practice they are rare.

So even in a huge pile of mail, everything would have to be reprocessed. Since it's so rare, I'm definitely going to set up metrics to monitor when it does happen. Do you have any insight on how people store the mail? Do they actually use the UID to reference it or is it used as more of a cursor?