[Exim] Advice Needed on "Drop Box" mailbox

I am designing an app that will need to poll a mailbox for reply
confirmations. I will be using addresses of the form system+uuid@???
and want all messages delivered into a maildir located at
/var/spool/mail/system/.

I don't really want this Maildir to be world-writable or to have to create
a system user just for it.

What would be the smart way to do this?

Thanks,

A.

P.S. The location of the mailbox isn't really important.

--
Adam Sherman
Tritus CG Inc.
http://www.tritus.ca/
+1 (613) 797-6819