I am working on a C module to display MIME parts from a file or the
database and then combining it with a qmail maildirs configuration
and some integration between qmail and the OpenACS user database and
theoretically have a robust, high performance, fully OpenACS
integrated webmail solution.
This would mean ACS and the mail server would run on the same
machine or at least share a file system but it would allow you to
use any existing qmail solutions for pop, imap, and smtp.
I can already read and display mime parts from a stored message
using the reformime utility from the sqwebmail package and the
ns_returnbinary command from my nsbinarysupport module. (it is at
http://www.vorteon.com/download/)