Know-how:
* hold shift, when "reply"-ing or "write"-ing to switch from HTML to plain-text writing mode.
Thunderbird Addons (plugins, extensions) used and liked:
Enigmail
ImportExportTools NG
Manually sort folders
Owl for Exhcange
(purchased it)
Remove Duplicate Messages (Alternate)
ThreadVis
Toggle Word Wrap
CardBook
CardDAV contacts synchronization (from NextCloud to ThunderBird)
Books: