Setting up a CNAME record for any of the domain names or subdomains that you've got within a hosting account will allow you to forward it to a different domain/subdomain. The forwarded domain name will lose all of its records - A, MX etc, and will take the records of the Internet domain it's being pointed to. In this light, you can't set up a CNAME record to direct your domain to a third-party provider and retain a functional email service with the first hosting provider. Additionally, it is very important to know that a CNAME record is always a string of words rather than a number as it's generally mistaken for the A record of the domain name being forwarded. One of the main uses of a CNAME record is to forward a domain you own through one company to the servers of some other company in case you have set up an Internet site with the latter. By doing this, the website will appear under your own domain name, not under some subdomain provided by the third-party company.