I hear good things about Obtuse SMTPd. I've used Postfix in the past, but that's really overkill.
I would have said postfix for mail proxying - the /etc/postfix/transport table is really quite flexible and easy to setup.
simon, give postfix a go - I can post a sample transport/mail host setup if you like
dave -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
