Click Help>moretroubleshootinginformation, then scroll down to 'Profiles', click about:profiles and the location will be displayed. Unless changed by you, the default setting is at c:\userid\appdata\roaming\thunderbird\profiles. That setting also applies to later versions. My response assumes you are using Windows.

David, Thanks, I've found it. Can you confirm that, if I back this up, I am backing up my message base as well as my settings? Alan.

That's the place. if you look there in File Explorer, you should see a Mail folder (for POP mail) and an IMAPMAIL folder for IMAP mail. In those two you should see your email accounts and mail folders. Be sure to copy it when Thunderbird is not running; otherwise, you will lose several components.

David, I'm confused again. I have a folder C:\Users\Admin\AppData\Roaming\Thunderbird that has a subfolder Profiles. It also has a subfolder Thunderbird (so we have Thunderbird off Thunderbird). The second Thunderbird folder also has a subfolder called Profiles (C:\Users\Admin\AppData\Roaming\Thunderbird\Thunderbird\Profiles). Do you know which Profiles I should be backing up? Alan.

Just the one that is displayed from first post. Those others are likely profiles that were incorrectly stored there. Many people think that location is special, but in fact your profile can be stored anywhere you want, whether the C drive or another drive.

What you can be do for your self confidence is to MOVE (not copy) that thunderbird\thunderbird\profiles subfolder elsewhere and restart TB. I think you'll find it works fine without that excess.

David,

Thanks for your comments, particularly the one about closing Thunderbird before backing up. I wouldn't have known to do that. I've removed the spare Thunderbird folder and the Thunderbird program seems quite happy without it.

I found the Mail folder at C:\Users\Admin\AppData\Roaming\Thunderbird\Profiles\yuzfnf2k.default\Mail,

Alan.

I was glad to assist. You're very welcome.