Rated 5 out of 5 stars

le Andrew ar Meith. 30, 2021 ·

If you want a 'Mark All Read' button for Thunderbird 78+ install https://addons.thunderbird.net/en-GB/thunderbird/addon/next-unread-group/ and change the value for mailnews.nav_crosses_folders in about:config from 1 to 2.