For our Hosted communities, you have two options. Use the entire Domain by pointing the Name Servers to us, or create a CNAME Record for a Subdomain of your primary Domain. (We can't use A Records in our new infrastructure.)
If you point the entire Domain to us, we can make MX record changes which will allow external mail hosting. (But that's all. Our packages do not include customizing the DNS otherwise.)
Using a Subdomain pointed here allows you to fully control your DNS, which can then be edited as you see fit for A or other CNAME Records, or to point to the mail host you want to use.