Thunderbird saves personal information such as messages, passwords and user preferences in a set of files called a "profile", which is stored in a separate location from the Thunderbird program files.

https://support.mozilla.org/en-US/kb/profiles-tb

You can move your profile across computers, or back them up to restore later.

https://support.mozilla.org/en-US/kb/moving-thunderbird-data...

I know about those (these are helpful links, thanks!). They are stored in different locations on different OS's, even different versions of the same OS. There needs to be a menu item called "Backup" where you give a path to back it up to, and "Restore" where you give a path where it was backed up to.

Reading the documentation on those links just proves the point :-)

The beauty of open source is that you can scratch your own itch. :-)

https://developer.mozilla.org/en-US/Add-ons/Thunderbird

Yeah, I already wrote my own compiler, editor, games, language, etc. How far do I have to go with this? :-)

I have always found the best strategy is to just backup the whole profile. The profile is very portable.