Setting up a CNAME record for any of the domains or subdomains that you've got in the hosting account allows you to redirect it to a different domain/subdomain. The forwarded Internet domain will lose all its records - A, MX and so on, and will take the records of the domain name it is being redirected to. In this light, you can't create a CNAME record to direct your domain to a third-party provider and keep a working e-mail service with the first hosting company. It's also essential to know that a CNAME record is always a string of words and never a number as it's frequently wrongly identified as the A record of the Internet domain being redirected. One of the main uses of a CNAME record is to direct a domain which you own through one provider to the servers of another provider in case you have set up an Internet site with the latter. By doing this, the Internet site will appear under your own domain address, not under some subdomain provided by the third-party provider.