Setting up a CNAME record for each of the domain names or subdomains that you've got in 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 is being pointed to. In this light, you simply can't set up a CNAME record to redirect your domain to a third-party provider and retain a working email service with the first provider. Also, it is essential to know that a CNAME record is always a string of words and never a number because it is regularly mistaken for the A record of the Internet domain being redirected. One of the major uses of a CNAME record is to direct a domain name you own through one company to the servers of another company when you have created a website with the latter. By doing this, the Internet site will appear under your own domain, not under some subdomain provided by the third-party company.