Creating a CNAME record for any of the domain names or subdomains you have within a hosting account allows 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 Internet domain it is being directed to. In this light, you cannot create a CNAME record to point your domain to a third-party company and maintain a working e-mail service with the first provider. Also, it is essential to know that a CNAME record is always a string of words and never a number as it is commonly wrongly identified as the A record of the Internet domain being forwarded. One of the main uses of a CNAME record is to point a domain address which you own through one provider to the servers of another company assuming you have set up a site with the latter. That way, the website will appear under your own domain, not under some subdomain provided by the third-party company.