Is there any change of connecting an Amiga mail program with Microsoft Exchange?
You will be stuck with POP3 or IMAP but that needs to be enabled on the Exchange server side of things. You will not be able to use the calendar invites/contacts features as such.
Exchange does come with a web front end for accessing your mail/calendar/contacts etc, think GMail and you could always leveraging that. Again, that's if it is enabled on the Excahnge server.