Setting up a CNAME record for any one of the domain names or subdomains that you've got in the hosting account will allow you to point it to a different domain/subdomain. The forwarded domain will lose all its records - A, MX etc, and will take the records of the domain it's being pointed to. In this light, you simply can't set up a CNAME record to point your domain to a third-party provider and maintain a working e-mail service with the first provider. Additionally, it is very important to know that a CNAME record is always a string of words and never a number because it is regularly mistaken for the A record of the domain name being forwarded. One of the main uses of a CNAME record is to direct a domain name you own through one company to the servers of some other company assuming you have set up a site with the latter. This way, the site will appear under your own domain name, not under some subdomain provided by the third-party provider.