DNS issues with domain alias

[carterbeech]

I have a domain A aliased to a domain B. I want A to use a third party mail service off-server and set up the MX records accordingly. In the alias prefs, I turned OFF the setting for mail as that wants to push the mail back onto domain B, not my third party mail service.

It doesn't work. Using NS lookup services, my MX record doesn't show up at all.

I'm running 8.1 on a linux box.