The simplest backup method is to copy the Thunderbird folder, which contains all the data for all profiles. The (hidden by default) location in W10 is:

C:\Users\windowsusername\AppData\Roaming\Thunderbird

To restore it to the same or another computer, simply replace the Thunderbird folder with the backed-up copy.

https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer

Another (Windows) option is to use a program like MailStore to continuously archive TB mail. But the other method backs up all data, including contacts, calendars, add-ons, feeds, settings etc.

Thank you. I used your simplest method, with help from the following help page https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_where-is-my-profile-stored I used the %APPDATA% approach in order to find my profile following your first suggestion as in "the (hidden by default) location in W10". My W10 Acer laptop is in German, and I am the only User ("Benutzer"), so the %APPDATA% route simplified finding the hidden file : " %APPDATA% is shorthand for the C:\Users\<username>\AppData\Roaming\ folder, which depends on your Windows user account name." There I found " Roaming > Thunderbird > Profiles ". The profile folder contains a file with 8 characters, in this case 6 letters and 2 numbers. I take it that this is the file to highlight - right-click and copy to an external disc. When it comes to restoring this profile, I would use the same procedure in reverse as it were : from the external hard disk to the hidden file on Drive C.

So basically I followed your: "The simplest backup method is to copy the Thunderbird folder, which contains all the data for all profiles. The (hidden by default) location in W10 is: C:\Users\windowsusername\AppData\Roaming\Thunderbird To restore it to the same or another computer, simply replace the Thunderbird folder with the backed-up copy."

As I only wanted to do a trial run, I left the Thunderbird program running so that it could not complete the copy, but will close it when I actually make the copy on an external disc.

Sorry to be so long-winded, but does that sound like I got it right?

Almost. While it's true that all the user data is contained in the profile folder, the Thunderbird folder also includes the all-important profiles.ini file that points the TB program to the location of the profile folder. It's a lot easier to copy your data to another computer or restore to the current one if you deal with the Thunderbird folder - and it doesn't require any significant extra space.

The same method applies to the ...\Roaming\Mozilla\Firefox folder.

Thank you very much, especially for the key .ini file point. In the AppData\Roaming\Thunderbird I see the following files : Crash Reports, Pending Pings (empty) , Profiles, and profiles (the all-important .ini file....of 122 Bytes!) So whenever I want to make a backup every 3 months or so, I just copy and paste this entire Roaming\Thunderbird folder onto external disk? Good.

BTW I see I downloaded the Mailstore App a few months ago to try it out. Whether I did that correctly or not I don't know, but it took AGES. In fact I cannot even find the folder it created on the same external disk. Your method just took a about 2 minutes to copy and paste externally maximum. While you are there, I would be most grateful if you could tell me where I would find the Mailstore App on my Drive C, so that I could either delete or uninstall it.

I don't have MailStore installed, but I'm sure you can remove it by right-clicking the icon in the Start menu, Uninstall.