I thought I'd post this here to help anyone having trouble setting up an @aol.co.uk in Thunderbird using the new OAuth2 authentication that AOL are forcing you to use now. As it appears there is an issue in Thunderbird with @aol.co.uk email addresses but @aol.com email addresses work fine. I recently received an email from AOL saying: ''We’ve noticed that you’re using non-AOL applications (such as third-party email, calendar, or contact applications) that may use a less secure sign-in method. To protect you and your data, AOL will no longer support the current sign-in functionality in your application starting on 20 October 2020. This means that you will need to take one of the steps below to continue using your AOL Mail without interruption. '' So I followed all the instructions to remove my AOL account in Thunderbird and re-add it. However, on the first dialogue box you fill out in Thunderbird to setup an account, I entered my name, email address and password, then clicked "Done", and then I waited whilst I got the "Looking up Configuration" message and Thunderbird populated all the settings for me, but the settings were not correct. For some reason when you try to setup a @aol.co.uk email address in Thunderbird it populates the incoming imap and outgoing smtp settings as "imap.mail.yahoo.com" and "smtp.mail.yahoo.com". I thought this seemed very odd but I continued on clicked the "Done" button and sure enought I was then presented with the sign in page for Yahoo and not AOL. So I cancelled the setup and started again, entered my name, email address, and password, clicked continue, waited for Thunderbird to populate the settings again, and again it populated the imap and smtp addresses with the details for Yahoo not AOL. So this time I clicked the "Manual Config" button removed the Yahoo details and entered the Imap server as "imap.aol.com" and smtp as "smtp.aol.com", clicked "Done" but it still took me to the Yahoo sign in page even though I'd entered the AOL imap and smtp settings. I emailed AOL about this and I was emailing them backwards and forwards for a 30 day period and they've been unable to find a solution, and eventually they've just washed their hands of the problem saying they don't offer direct email support for AOL mail, and just provided a lot of links to support pages that offer no help at all. WORKAROUND: After spending some time looking at this I finally found a workaround for the problem. When you go to add a new account in Thunderbird and it asks for name, email address and password, DO NOT enter your email address as @aol.co.uk, instead enter it as @aol.com and fill out name and password as normal, then click continue. Thunderbird will then populate the correct details for imap and smtp, but you still have to make some manual changes. Click the "Manual Config" button, DO NOT change the email address field, leave your email address ending @aol.com, if you try changing this at this point Thunderbird will re-populate the wrong settings again. All you need to do is to change the incoming and outgoing usernames from@aol.com back to @aol.co.uk then click "Done". Now you will get the correct AOL sign in page, you can enter your sign in details and Thunderbird will be able to setup the account. Once the account is setup, just go back into the setting for the account you created and change your email address back to @aol.co.uk So basically for some reason when you try to create an account for an @aol.co.uk email address, Thunderbird is populating the wrong Imap and SMTP details from whatever database it pulls them from. I'm assuming this is something that only Mozilla can correct. Manually changing the incorrect details will not resolve the problem, you have to basically trick Thunderbird by entering your email as @aol.com instead of @aol.co.uk to get the correct aol settings populated, and then make manual changes from there. As far as I can see it looks like the reason you can't just make manual changes is because of OAuth2. It looks like when Thunderbird automatically pulls through all the incorrect details, you can manually change the imap and smtp settings, but the URL it sends you to to sign into your account is not updated so it still sends you to the wrong URL.