Subdomains

I have a domain simplyschools.net. I have several schools that want their
own email address say user@school1.simplyschools.net. Few questions:

1. DO I setup one zone file simplyschools.net and put A records in that zone
file for the mail server:

mail.school1 A 65.66.8.103
school1 CNAME mx1.duracom.net.

What will the zone file respond with when asked what are the mx records for
school1.simplyschools.net? Should I do this another way.



Thanks,


Kris