Draft mail is the WordPress custom post-type of databases.
Ultimately all productivity apps for privacy focused folks trend towards a locally synced database containing stuff. A database searched with an interface you already use. This is e-mail, if that wasn’t already ruined by untrusted parties.
- Notes: mail in a folder
- Bookmarks: page content referenced by a URI as mail in a folder.
- Todos: mail in a folder
Some of these use a man in the middle process to filter content, and high volume incoming / outgoing mail might get your account in trouble. So there are webservices with paid options to sustain them, with data export and privacy concerns.