Gnus is the package I use for mail and news.
nnmaildir is a maildir backend for Gnus.
I've added rudimentary
Mail-Followup-To support to
Gnus (message.el, to be specific). My code is included in Gnus
5.10 and later; if you're using 5.8.8, you can get the corresponding patch
here. But there are
probably some bugs in that patch that have since been corrected; I'm not
maintaining this patch separately.
nnnil is an empty, read-only backend for Gnus. It's useful as a primary server when you want all your real servers to be secondary or foreign. I committed it to Gnus CVS on 2002-03-05; Gnus 5.10 has since been released. If your Gnus is older than that and doesn't already have nnnil, you can get a copy from CVS and use it with your Gnus. nnnil ignores whatever server name and server parameters you give it.