Creating a CNAME record for any of the domain names or subdomains you have in a hosting account will permit you to point it to a different domain/subdomain. The forwarded domain name will lose all its records - A, MX and so on, and will take the records of the domain name it's being forwarded to. In this light, you simply can't create a CNAME record to point your domain name to a third-party provider and keep a working e-mail service with the first hosting provider. Additionally, it is essential to know that a CNAME record is always a string of words and never a number as it is regularly wrongly identified as the A record of the domain name being redirected. One of the primary uses of a CNAME record is to point a domain name which you own through one company to the servers of another company assuming you have set up a site with the latter. That way, the website will appear under your own domain address, not under some subdomain provided by the third-party company.