I opened Thunderbird today and found that it had downloaded -- or at least was showing -- two copies of many emails. This affects only one email address of the three addresses I've got in Thunderbird; but it affects email going back years. (I've been meaning to archive my old emails but haven't gotten to it yet.) These old double emails were not there before. I tried closing Thunderbird and rebooting my computer and it is not doubling the emails downloaded since then. This account is on AOL and set to use POP. One thing that is confusing about the old emails doubling up is that I know they are no longer on AOL's servers. For some reason, AOL lost my email from before Jan 2018 this summer. I was relieved to discover that when I installed Thunderbird, I'd not done as recommended and used IMAP for this account, so my old email had gotten saved to my computer. (I suppose it's possible that I wiped it off AOL, but I have Thunderbird set to leave mail on the server, and email from after January is still there.) Sorry if I sound a bit inept, confused, and confusing. I'll appreciate whatever help anyone can give me. Thanks.