thank you!, TEBE is what I waited for.
The information on the shut-down option says, that the backup will run when TB is closed, not restarted.
The opposite is the case. TEBE runs the backup when TB is restarted, but not when closed.
Please fix this. Thank you.
It's a bit more tricky:
The backup only starts when restarted with the extension "Restart Thunderbird".
The TB restart button in the add-on window doesn't make TEBE run.
But the backup at shut-down is not run anyway, even if this extension is deactivated.