With theGeneraltab selected on the left, scroll down to theIncoming Mailssection.
go for the box next toShow an alertso it’s enabled.
If you’d like, selectCustomizeto edit some additional options, then chooseOKto save.
snag the Apple menu and then chooseSystem tweaks(orSystem Preferences).
pick the toggle next toAllow notifications.
In some versions of macOS, this is calledAllow Notifications from Thunderbird.
Select any other options you want to enable, like to show new email alerts on the lock screen.
Changes are saved automatically.
