question about Maildir and Webmail

[Umum Wijoyo <umum@lola.ee.itb.ac.id>]

Hi!
I'd like to ask how to set up a Maildir format for my users.
Is /var/spool/mail/$USER an mbox format or a Maildir format? I think it's
an mbox, right? So how do I convert it into a Maildir format? What are the
benefits?

My next question, how do I set up a Webmail facility for my users? Is
there a Debian package for it? Is it the "imp" package?

Thanks a lot.

Umum Wijoyo