NOTE: This method only works for POP account, not IMAP account
At the Thunderbird, go to Tools > Account Settings . If Tools menu does not appear, press the Alt button on your keyboard.
Click on Server Settings on the account that you want to leave a copy of mail
Under Server Settings , check on "Leave messages on server"
Then click on the OK button.
NOTE: If you would like to remove the mail after several days, you can check on " For at most ? days "
At the Thunderbird, go to Tools > Account Settings . If Tools menu does not appear, press the Alt button on your keyboard.
Click on Server Settings on the account that you want to leave a copy of mail
Under Server Settings , check on "Leave messages on server"
Then click on the OK button.
NOTE: If you would like to remove the mail after several days, you can check on " For at most ? days "
Updated on: 27 / 02 / 2019