To add to the above, if it were a mailbox on your computer, if you open:
user/Library/Mail/V3/Mailboxes and then open Time Machine, you should be able to find anything from the past.
Note: I'm not sure in the above path if "V3" will be your designation. I have a V2 also, but "Mailboxes" showed up in my V3. Look around.
On a Mac since 1984.
Currently: 27" iMacs, Macbook Air, macOS 10.15.x,; iPhones, iPods and iPads galore!