tracking message ids with nnmaildir?

[Antonio Carzaniga <antonio.carzaniga@usi.ch>]

The following message is a courtesy copy of an article
that has been posted to gnu.emacs.gnus as well.

I have trouble tracking message ids for messages stored in Maildir
groups (e.g., to automatically split follow-up messages to the same
group).  In particular, neither the nnmail cache nor the registry would
pick up the ids of messages spooled to a Maildir group through Gcc.

In trying to figure this out, I noticed that nnmaildir does not track
message ids at all, whereas all other mail back ends track every message
they accept through nnmail-cache-insert, which is where the registry
hooks into.  This looks like a bug, no?  Am I missing something?  How
can I track messages automatically spooled to Maildir groups?

Thanks a lot for your help!

-Antonio