Setting up a CNAME record for any one of the domain addresses or subdomains that you have within a hosting account will allow you to point 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 Internet domain it is being pointed to. In this light, you simply can't set up a CNAME record to direct your domain to a third-party company and maintain a functional email service with the first hosting company. Also, it is very important to know that a CNAME record is always a string of words rather than a number because it is commonly mistaken for the A record of the Internet domain being redirected. One of the main uses of a CNAME record is to forward a domain address that you own through one provider to the servers of some other company when you have created a website with the latter. That way, the site will appear under your own domain name, not under some subdomain provided by the third-party company.