[Dovecot] How to stop POP clients from downloading mail after directory corruption

[Frank Church]

Transferring my email from a Courier server, as well as some
corruption in my dovecot installation caused all POP mails to be
downloaded again.

I surmised that the dovecot-uidlist file was not present in the first
instance, and was probably out of sync in the second.

Is there a way to do some reindexing and uid-list regeneration that
can stop the problem from occurring?

 - Frank