Thunderbird seems to struggle with more than 2000 or so messages in the inbox, I've discovered. I've currently got about 2100 and little problems start cropping

Thunderbird seems to struggle with more than 2000 or so messages in the inbox, I've discovered. I've currently got about 2100 and little problems start cropping up - currently it marks all incoming messages as junk even though I have all the junk filters disabled on every account. It would be worth it for me to get the inbox down a bit, at least!