Sorry, I'm coming into this late. Early on, Kevin McCarthy said:
Native support for multipart/alternative composition isn't in my todo list.
Too bad -- that would be conceptually clean, to generate multipart/alternative as part of composition.
Mutt runs an external text editor to compose plain text; it could do the same for this -- run some external composition program that would return both HTML and plain text. That external program could be anything, could be user's choice. It could be a GUI HTML editor that generates HTML and plain text in parallel from what the user does. It could be a shell script, that runs a text editor where the user types Markdown, and then converts that to HTML and returns both.
From there, I guess Mutt would treat that multipart/alternative the same as a simple body part of plain text: build a MIME tree around it, with attachments and GPG signature. Would that work?
