Creating a CNAME record for any of the domains or subdomains that you've got within a hosting account allows you to redirect it to a different domain/subdomain. The forwarded domain name will lose all its records - A, MX and so forth, and will take the records of the domain address it is being forwarded to. In this light, you cannot create a CNAME record to forward your domain to a third-party provider and keep a working email service with the first hosting provider. Additionally, it is very important to know that a CNAME record is always a string of words rather than a number as it is generally wrongly identified as the A record of the Internet domain being forwarded. One of the primary uses of a CNAME record is to forward a domain which you own through one company to the servers of another provider when you have created a site with the latter. This way, the site will appear under your own domain name, not under some subdomain provided by the third-party provider.