I just found this thread from June while looking to resume a draft saved
from another program (dovecot) and which was given the 'draft' tag by
synchronization from Maildir flags.  Mark, thanks!

I *think* all I have to do to deal with other clients accessing the
Maildir through IMAP is to remove 'Message-ID from message-deletable
headers, because other clients may be watching for that---though this
only matters if the draft is resumed and postponed again, rather than
deleted.

Does that sound right?

      (when draft
       (notmuch-message-unquote-some-mml))

One comment here: anyone using maildir flag synchronization will have
items with tag:draft but no quoted MML.  To help them reasonably
*discuss* quoted MML, even when working from a mix of notmuch and other
MUAs, can this use a distinct tag?  For example, tag:quoted-mml?

Thanks,
Brian