Setting up a CNAME record for each of the domain names or subdomains you've got within a hosting account allows you to direct it to a different domain/subdomain. The forwarded domain name will lose all of its records - A, MX and so forth, and will take the records of the domain address it's being redirected to. In this light, you can't set up a CNAME record to direct your domain name to a third-party provider and maintain a working e-mail service with the first hosting company. Also, it is very important to know that a CNAME record is always a string of words rather than a number as it's generally wrongly identified as the A record of the domain address being forwarded. One of the primary uses of a CNAME record is to forward a domain name you own through one provider to the servers of another company when you have set up a website with the latter. This way, the site will appear under your own domain address, not under some subdomain provided by the third-party company.