Great work!

> Yeah, I can add it so the folder can be changed.  I figured this was just the
> start of things.  Really we should be able to fcc it to our upstream provider
> sent mailbox too.

I would appreciate an option to configure the "sent" box per provider. I
implemented this feature in this patch:

id:1420891384-992-4-git-send-email-telenczuk@unic.cnrs-gif.fr

The way it works is that it reads a mapping between the email-addresses and sent 
dirs from .notmuch-config. Then it parses the "from" header of the sent message
and "notmuch inserts" the message into the directory associated with the "from" address. 

It is not a fully polished patch. Perhaps we could merge the two to get something more final.

Bartosz