Timo Sirainen wrote:

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Any idea what that is? I did no special operation, just selected a mail to read with thunderbird (1.06). After restarting TB it worked. It has something to do with maildir filename changing (by another Dovecot process?) while Dovecot is reading the maildir. A bit tricky to fix..

It can only be another Dovecot process, nothing else is changing files there. TB opens multiple connections to the IMAP-Server by default, so maybe by clicking around a little too fast, the message was changed to "seen" by one process, but the other process wanted to access the message with the old filename in the old directory. Trying to acesss the file in both cur/ and new/ with the different Maildir flags could probably help, but is no complete solution and quite clumsy. What fix were you thinking of?

I think I'll change TB to keep only a single connection, so this should not happen again. Never really understood what multiple IMAP connections are good for, anyway.