Must I transfer my domain REGISTRATION to comcast in order to use it with my exchange email?

the wording / steps in your support articles are not exactly clear.  To use your exchange email with a domain i already own, must I actually transfer  the domain registration from my current registrar, GODADDY, to Comcast, or am i only "transfering" where the domain points so it can be "activated" on your platform.? 

your Activate Domain section appears to be creating an actual tranfer, whereas your email only set up instructions seem to suggest I am just changing my MX records at my current registrar/dns provider.

Thank you in advance for your clarification