Creating a CNAME record for any one of the domain names or subdomains you have in the hosting account allows you to redirect it to a different domain/subdomain. The forwarded Internet domain will lose all of its records - A, MX etc, and will take the records of the domain it is being pointed to. In this light, you simply can't create a CNAME record to forward your domain to a third-party provider and retain a functional e-mail service with the first hosting company. It's also very important to know that a CNAME record is always a string of words and not a number as it's often confused with the A record of the Internet domain being forwarded. One of the major uses of a CNAME record is to point a domain that you own through one provider to the servers of another provider in case you have created a site with the latter. This way, the site will appear under your own domain, not under some subdomain provided by the third-party provider.
