Setting up a CNAME record for each of the domains or subdomains that you've got within a hosting account will allow you to forward it to a different domain/subdomain. The forwarded domain address will lose all of its records - A, MX and so forth, and will take the records of the Internet domain it is being redirected to. In this light, you simply can't create a CNAME record to forward your domain to a third-party provider and retain a working e-mail service with the first 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 commonly wrongly identified as the A record of the domain being redirected. One of the primary uses of a CNAME record is to direct a domain address that you own through one provider to the servers of another company in case you have created a site with the latter. This way, the website will appear under your own domain address, not under some subdomain provided by the third-party provider.