[Dovecot] Purpose of files under .imap

I've got a user with an unusable account. Tbird just sits in a loop endlessly logging in over and over when a particular folder is selected.

What files under .imap associated with that folder can be safely deleted? What's stored in all of them?

I see all of these:

.customflags dovecot.index dovecot.index.cache dovecot.index.log .imap.index .imap.index.data .imap.index.log .imap.index.tree