With a few thousand emails, it just bogs down constantly. Delete a message and it can take, oh, 2 minutes for one. Click and take a pizza break. It can come back and perform fairly reasonably. But I'd never call it "snappy". Aside from that, for no particular reason, Thunderbird decided after one of its updates in the past 8 months that it would delete things and not put them into trash. I found this out when I needed to recover from trash and .... gone. And then there was the time when I decided to empty the trash folder and Thunderbird deleted all emails in all folders, except those I had take out and stuck in folders outside of that account. But mostly, it's slooooooooooooooooooooooooooooooooooooooooooow. And getting slower...