A couple of months ago Thunderbird started being very slow in multiple situations. I use POP3 and download all mails. I have fairly big mailboxes, some of them up to 2½ GB. 1) Downloading e-mails is slow. But the worst is this one: 2) Clicking on unread mails first time. This can easily take 10 secs, where the app goes "not responding" and finally "Loading message...." With 10 new mails, it is a lot of wasted time. 3) Dragging mails from one mailbox to another Some of the same behaviour as above. I have tried to compact mailboxes, but that doesn't help. I am on release 128.4.1esr (32-bit), windows 10.