I have many filters set up in Thunderbird, and they're great when they work, but I cannot run (at least some of them) on entire folders or "large" numbers of messages. I'm not sure what the limit is, but it'll do a few hundred and not a few thousand. If I select a message or a few dozen, it works. If I select, say, 2000 messages, and tell it to run filters on selected messages, it just doesn't do it, or starts to do it (shows the progress indicator) but stops before it's done and doesn't move anything. Additionally, once I exceed this limit, filters don't seem to work at all until I restart Thunderbird.

The main filter I know of that has this problem (which has been a great problem for me) is one to move old mail from one box to a local folder. It selects on addressee and age in days. It works fine if I do a message or two, or in very small batches, but not en masse. If there's one thing computers are good at, it's en masse, so this is frustrating.