I have a problem with latest Thunderbird on OSX (El Capitain) frequently hangs with "spinning beachball", for minutes at a time, several times an hour. It's pretty unusable right now. Last time I noticed that my "Archives" seemed to be downloading, and I don't even use the Archives (it's an IMAP account) and I realized that it looks like all of my inbox messages have been duplicated to my Archives folder a couple days ago. I'd like to just blow out or empty the Archives, I think this could be part of my problem (I also noticed this account Inbox was "checked" for "offline access" which I've since disabled.