Setting up a Site Server with Jaguar
Subject:   can't connect to imap server
Date:   2003-11-22 16:13:28
From:   anonymous2
Response to: can't connect to imap server

I didn't know what to use either but fortunately something said elsewhere in these comments allowed me to correctly guess "localhost". Seems obvious now but there you go. Use this for both incoming and outgoing server names.