Setting up a CNAME record for any of the domain names or subdomains you've got in a hosting account will permit 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's being redirected to. In this light, you simply can't set up a CNAME record to forward your domain name to a third-party provider and retain a functional email service with the first provider. Additionally, it is important to note that a CNAME record is always a string of words and not a number as it's regularly wrongly identified as the A record of the Internet domain being redirected. One of the main uses of a CNAME record is to direct a domain that you own through one company to the servers of some other company assuming you have set up a site with the latter. By doing this, the Internet site will appear under your own domain, not under some subdomain provided by the third-party provider.