[Baertram]

If you are searching for a solution/working addon:
FCO ChangeStuff got that features with favorites recipients, subjects, texts and even remembers the lasts send values (and provides a "last send" history) if you enable it at the settings.

Check FCO ChangeStuff settings -> mail

And directly at the mail send panel top left you will see the "mail settings" chain icon then where you can click and see the contextmenu with the possible settings.
Right clicking the subject, recipient, text fields add more options then to add to favorites, remove from, last send data, etc.

That way sending multiple emails to the same recipient, and remembering + reusing last send works very well.



If you are searching for the code check the src/FCOCS_mail.lua files, but please provide proper credits in your addon then if you release it. Thanks