Dovecot generates Error: Threading lost Message ID in dovecot.log
Problem is only with one Maildir. This Maildir cannot be accesed through webmail (in this case Roundcube), error in webmail after log in:
Server Error: UID THREAD: Internal error occured. Refer to server log for more information.
The only suggestion I've found is here: http://www.dovecot.org/list/dovecot/2013-August/091939.html but I still don't know what causes the problem, how to fix it and how to avoid it in the future, so any suggestion appreciated.
Kind regards!
And finaly I've found the solution. Somehow file dovecot.index.thread was corupted and causes the problem. I've deleted file dovecot.index.thread, the file was rebuild then properly, and problem was solved.