I have been using Thunderbird for a year. It is ok, but some problems are borderline un-tolerable. I have ~3500 emails in my IMAP account. I would like to keep more for a deeper search, but ok - I could handle that. And once in a while, about every month, I am doing something and the Thunderbird decides to re-download all my messages. And it locks me out of all emails for about 2 hours while this process is ongoing. I cannot open emails, I cannot answer - nothing. I have no "cleaning" software, I do not mess up with the database file. Is there a way to avoid this re-download? If not, is it possible to avoid the lock-out, to get emails usable while it does it - for example, download the most recent emails first and make them visible at least?