This folder-based searching is very handy.  However, I have a scenario
in which I'd prefer to consolidate mail to multiple addresses into one
or a small number of physical mail folders.  Thus, what I really want
to search on is not the mail folder name, but the Delivered-To:
header.

Can someone tell me if there is any easy way to restrict a search to
the Delivered-To: header, or to add custom header support to notmuch?

Sorry if this is a very basic question.  I've just started checking
out notmuch and really like what I see so far.  My inability to figure
out how to search unambiguously for Delivered-To headers looks like it
could be the biggest obstacle to switching from Wanderlust (which lets
me customize search for arbitrary headers listed in
elmo-msgdb-extra-fields).

Thanks.