Mdaemon to exchange 2007

Hi, am moving from mdaemon to exchange 2007 in sbs 2008, there are only 3 local users on the network but there are about 20 clients that get there email through the mdaemon server at present. Not sure if I need to set up an account for each user in the sbs 2008 console or I can just add the users to the exchange, any help and advice would be gratefully appreciated.