Creating a CNAME record for any one of the domain names or subdomains you've got within a hosting account will allow you to forward it to a different domain/subdomain. The forwarded domain address will lose all of its records - A, MX and so on, and will take the records of the domain name it is being redirected to. In this light, you cannot set up a CNAME record to direct your domain to a third-party provider and maintain a functional e-mail service with the first hosting provider. Also, it is essential to know that a CNAME record is always a string of words and never a number as it's frequently confused with the A record of the domain being forwarded. One of the major uses of a CNAME record is to point a domain name which you own through one provider to the servers of some other provider if you have created a site with the latter. This way, the website will appear under your own domain, not under some subdomain provided by the third-party company.