Álvaro Ramírez
mu4e as macOS mail composer
Via Using Emacs as Default Mailer on macOS, a tiny script to handle mailto: links.
From /Script Editor, save following script as Application (MailOnEmacs.app). From Mail.app, Preferences -> Default email reader and chosse MailOnEmacs.app.
on open location myurl tell application "Emacs" to activate set text item delimiters to {":"} do shell script "/path/to/emacsclient --eval '(browse-url-mail \"" & myurl & "\")'" end open location