Threads that don't play nice with any other e-mail client, where Thudnerbird drafts would just fill up your thread history to the point it wouldn't make sense.

Threads that don't play nice with any other e-mail client, where Thudnerbird drafts would just fill up your thread history to the point it wouldn't make sense. And terribly broken IMAP support that wouldn't use IMAP labels, but instead transfer a separate copy of an e-mail to multiple folders if it had multiple labels. I thought Gmail was amazing when I first got it, and by 2012 I started running my own e-mail server when I realize it was a usability nightmare.