unexpecteg tag, and uidvalidity changes

[Peter P. <pet...@fa...>]

Hi list,

I am happily syncing about ten different email accounts with mbsync.
Strangely a few of them do change their uidvalidity almost once every
three months.

Now when re-syncing, the process stops after a few synced mails with the
message:

	IMAP error: unexpected tag XYZ

where XYZ is any random gibberish, sometimes parts out of email headers
and bodies. Upon re-running the same sync, the contents of XYZ change.

This is currently on a Microsoft Exchange IMAP4 server, and has also
happened on a Groupwise server in the last days, with isync isync 1.1.2

On a more general scope, as I do have to delete the affected folder's
.mbsyncstate files, and re-sync/delete duplicates every time, I wonder:

What could be common reasons for the servers to change their
uidvalidity?
Why is this an issue to me with mbsync, but not with something like
thunderbird, or mutt-accessing-imapServer-directly?
Is there any better, yet still safe and simple, way to work around
changed uidvalidities, or even more permanent fixes?

Thanks for all ideas and comments!

cheers, P