For about the last 2 weeks, Thunderbird has been automatically marking new emails as "read" as soon as they are recieved. I have checked the "options" setting and this has not changed, wiith the option to do this unticked. I've tried ticking the box, restarting then unticking and restarting again, but it makes no difference. This only affect emails from a "pop" server. Messages from my 2 IMAP email accounts don't have this problem.

Also, for a long time now, my "read" emails have not been deleting from the server. I have this set to 90 days, but it's not happening.