Setting up a CNAME record for any of the domain names or subdomains that you have within a hosting account allows you to direct 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 name it is being directed to. In this light, you can't set up a CNAME record to forward your domain to a third-party company and keep a functional email service with the first provider. It is also essential to know that a CNAME record is always a string of words rather than a number as it is regularly mistaken for the A record of the domain name being redirected. One of the primary uses of a CNAME record is to direct a domain which you own through one company to the servers of another provider when you have set up a site with the latter. In this way, the website will appear under your own domain, not under some subdomain provided by the third-party company.