Hi - I've got two copies of Dovecot installed on my server (don't worry, talking to two different sockets for authentication, with two different sets of filenames using options in configure), and I found at least one instance where the index file for my INBOX (on my own account, in fact) got corrupted. So badly so that when I connected via IMAP and selected my INBOX, it said there were no messages there - but if I logged in via sqWebMail (ugh), it said all my messages were there. Note that it didn't give the 'NO can't use index file' message. I moved the .INBOX directory to another filename, and then re-logged in and found that all was well (it regenerated the index files correctly).
Would my old, corrupted index files be of any use to anyone? I still have that directory sitting somewhere. Is it perhaps 'bad' to run two copies of Dovecot? I don't know exactly what I was doing, but I can easily imagine accessing one of my Dovecots using my webmail setup, and one using straight IMAP - is that an unsupported setup?
I'd also be happy to discuss why I'm using two copies of Dovecot, but that's a whole other discussion :)