I occasionally do this by combing at(1) with mhmail(1) or send(1). MH
is designed to integrate with the Unix shell so instead of MH growing
features, I'd initially look more at combining cron(8) with a shell
script that sends email whose time has come. Perhaps that's detected
by the name of the draft folder where they reside, or a header that's
--searched for with pick(1).
I'm with Ralph here; it seems like nmh already has these tools to leverage.
But it would be interesting to hear whatever solution you come up with.
On a related (organizationally, but technically probably orthogonal)
note, I have been thinking that it would be nice if nmh supported
responding to Disposition-Notification-To: headers somehow.
https://tools.ietf.org/html/rfc8098#section-2
I think the technical issues are relatively straightforward, except maybe
that we'd need to make sure messages are marked so they don't ever get
notified multiple times. There are some UI issues to work out; like,
do you want to do some action to repond to that? Or have it done
automatically? The latter might be hard today, but the former should
be easy.
That's where I was going.
I would use a custom post that looked for some header, and if found, would
move the outgoing email to some directory.
A cronjob would for f in SOMEDIR/`date +something`/*; do post <$f; done.
I would just caution you that "post" is really designed as a backend program,
and you have to be careful when you use it directly. I'd suggest you use
'send' instead.
--Ken