So did I a long time. But there's not really an Java based alternative
to cyrus, courier or dovecot.
James is experimental. Meldware Mail (
www.buni.org), based on JBoss,
seems to die.
You can also try Dwarf Mailserver (
www.gnome.eu). It's free but not
open source and not really production ready.
Recently I've found a communication suite at
www.coadunation.net but I
didn't try it yet.
It's disappointing. I hope this situation will get better.