[Dovecot] Purpose of files under .imap

[Kenneth Porter]

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