Setting up a CNAME record for any one of the domains or subdomains that you have within a hosting account allows you to direct it to a different domain/subdomain. The forwarded domain address will lose all of its records - A, MX etc, and will take the records of the domain address it's being pointed to. In this light, you cannot create a CNAME record to forward your domain to a third-party provider and keep a working e-mail service with the first hosting company. It is also 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 major uses of a CNAME record is to forward a domain name you own through one provider to the servers of another provider assuming you have set up a site with the latter. This way, the website will appear under your own domain name, not under some subdomain provided by the third-party company.