Hi,
I'm a pending grad student working on a project peripherally related to this, and Rafael pointed me to this discussion.
WING (http://users.ox.ac.uk/~mbeattie/wing/) is written in Perl and runs under mod_perl and Apache. It does IMAP and NNTP, and claims to scale well. It interfaces with an RDMBS.
The author, Malcom Beattie, is a pretty well-known Perl guy, though I can't vouch for the quality of this particular project since I haven't tried it myself yet.
-Ken
