Message Notes Plus allows to add notes to emails. The notes don't affect the email in any way.They are stored locally on your hard drive. The commercial version is no longer available. More info on mnpforum.alehro00.com and forum.alehro00.com.
Guys, please feel free to push your updates. Please keep changes as small as possible for the start. Since we don't have resource for thoroughfull testing. After some review I will publish the addon.
Recently I have added script to compose the xpi file. See cli folder.