I have a pretty weird way of composing replies and new messages: I like to be able to detach from the new message window. So I compose in a separate tmux session.
If you compose directly in mutt+vim without composing in a separate tmux window, does it work? (I would assume so, as I use mutt+vim and format flowed works fine).
I don't quite understand how your composing system works well enough to have a more meaningful comment.
- DLD
