Setting up a CNAME record for each of the domain names or subdomains 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 on, and will take the records of the domain address it's being directed to. In this light, you can't set up a CNAME record to forward your domain name to a third-party company and retain a functional email service with the first provider. Additionally, it is very important to know that a CNAME record is always a string of words and never a number because it is generally wrongly identified as the A record of the Internet domain being forwarded. One of the major uses of a CNAME record is to direct a domain which you own through one company to the servers of another provider in case you have created a website with the latter. That way, the Internet site will appear under your own domain, not under some subdomain provided by the third-party provider.