Backing up Thunderbird Emails is simple with SyncBackSE/Pro. Before we jump in and explain this process, there is one important consideration we would like to tell you about.
You can back up Thunderbird to the same backup destination every run, but watch out! If you manage to trash your Thunderbird mail completely, then the next time you start Thunderbird it will automatically create new standard folders (Drafts, Inbox, Sent, Templates and Trash). If your backup schedule kicks in after that, but before you restore the good data, then it will backup the new Thunderbird empty folders to your Thunderbird destination.
That will destroy the last backup of those folders but other email folders should still survive (see below **).
This might not be likely, but backup is about eliminating risk of data loss, so here's what to do. (You should look up the use of Variables in the SyncBack help documentation to clarify the following)
1) Create a separate profile for Thunderbird with the source being something like:
%APPDATA%\Thunderbird\
and a destination similar to:
d:\backup\%DAYOFWEEKNAME%\Thunderbird\
(of course you would use your destination drive letter, or use the %LABEL=% variable.)
2) Under the Advanced tab, section What to do if file is in the destination but not in the source, select Do nothing. DO NOT select Delete file from destination, or SyncBack will delete the good folders because they no longer exist in Thunderbird.
The profile tells SyncBack to do the backup into folder "backup", and sub-folder named Mon, Tues, etc, depending on the day of week, and sub-sub-folder "Thunderbird". So, all your Thunderbird backups (on Friday, for example) would go into a folder named "backup\FRI\Thunderbird". Now you have a daily backup for each of the last 7 days.
Of course, SyncBack is smart enough to know that, even though it is using a different folder, it is all part of the same backup scheme, and so SyncBack only backs up files that have changed. So, if some of your Thunderbird email folders don't change one day, those folders don't get backed up. That cuts down on the backup size and time.
Because of that, if you need to restore the email folders, first shut down Thunderbird. Then you will need to go through each of the seven daily backup folders, recovering the most recent email files. You can start with the oldest and copy all the Thunderbird files from the backup to the source. Then the next oldest, etc. When you have finished, you will have the most recent of each email folder. When you restart Thunderbird, everything should be in place.
By the way... use that %DAYOFWEEKNAME% idea for all the data folders where you want to retain some history. That way, you will always be able to go back to your last good backup copy.