Setting up a CNAME record for each of the domains or subdomains that you've got within a hosting account will enable you to forward it to a different domain/subdomain. The forwarded domain name will lose all of its records - A, MX and so on, and will take the records of the domain it is being pointed to. In this light, you cannot set up a CNAME record to point your domain name to a third-party provider and maintain a functional email service with the first hosting provider. Also, it is very important to know that a CNAME record is always a string of words and never a number as it's often wrongly identified as the A record of the domain address being forwarded. One of the major uses of a CNAME record is to direct a domain address that you own through one provider to the servers of some other company assuming you have set up an Internet site with the latter. In this way, the website will appear under your own domain name, not under some subdomain provided by the third-party provider.