I would like to discuss the feature ‘email into joplin’.
This feature adds a workflow to archive messages from your email into joplin.
Ideally, the user would forward a message to a catch-address. this is practically impossible without requiring the user to host a mail server.
The better option: The user can create a special configurable folder (i.e. /joplin) in his email account and move/copy messages intended for joplin in there. The desktop/terminal application, when syncing, could also login into this email account and pull all messages from this specific folder and import them, optionally parsing notebook and tags from the subject line (i.e. @notebook1 #tag1 #tag2).
This feature benefits from the existing HTML to MD logic.