Setting up a CNAME record for any of the domains or subdomains that you have in the hosting account will allow you to direct it to a different domain/subdomain. The forwarded Internet domain will lose all its records - A, MX etc, and will take the records of the domain it's being directed to. In this light, you simply can't set up a CNAME record to direct your domain name to a third-party provider and maintain a functional email service with the first hosting company. It's also very important to know that a CNAME record is always a string of words and not a number as it's commonly wrongly identified as the A record of the domain name being redirected. One of the primary uses of a CNAME record is to forward a domain address which you own through one provider to the servers of some other provider if you have set up a website with the latter. This way, the Internet site will appear under your own domain address, not under some subdomain provided by the third-party provider.