Restore mail in Thunderbird

the default mechanism is very lame
\r
bekapy:
— a copy of the folder with the current post ( %APPDATA%\\The Bat)
— copy branch The Bat from the registry ( .\\.\\RIT )
\r
all rose on HURRAH

ctrl+alt+shift+L
you have a terribly broken base, actually
in such cases it is better to transfer by copying as a comrade said in the first reply, and the transfer using the backup may give unpredictable results.
repair impossible through the "manage folders" and only the stupid transfer emails to another temporary folder and then removing the old folder database file and index, and move the emails back