Setting up 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 will lose all its records - A, MX etc, and will take the records of the domain name it's being redirected to. In this light, you simply can't set up a CNAME record to redirect your domain to a third-party company and maintain a working e-mail service with the first hosting company. Additionally, it is very important to know that a CNAME record is always a string of words and never a number as it is commonly mistaken for the A record of the domain address being redirected. One of the main uses of a CNAME record is to forward a domain address you own through one provider to the servers of another company assuming you have created a website with the latter. By doing this, the website will appear under your own domain, not under some subdomain provided by the third-party company.