Yes, that was fast! The answer makes sense too; I don't know why I didn't think of that (the "domain" can be "set up" in both places, and "served" from one place while the mail-exchange is handled from another) Duh! Must be having a really slow morning .
I'm thinking the only trick will be getting the MX records properly set where the domain is "managed", which will have to be handled with them. Thanks for sharing back what you learned; I appreciate it!