How to assign multiple email addresses in exchange 2003

we are currently running groupwise 7.0 and we are migrating to exchange 2003 standard.  on the current setup we have four schools each with their own post office in groupwise.  we want to duplicate this in exchange.  we only have one groupwise server and we will only have one exchange server.  each school has their own email address, i.e. school1@school1.edu, school2@school2.edu, etc.  how do i duplicate this on the exchange side??  is it as simple as creating different Recipient policies or is it something else like assigning different email address for the users in the schools??