Creating a CNAME record for each of the domain addresses or subdomains that you have within a hosting account allows you to point it to a different domain/subdomain. The forwarded domain address will lose all of its records - A, MX and so on, and will take the records of the domain address it is being forwarded to. In this light, you simply can't set up a CNAME record to direct your domain to a third-party provider and retain a working email service with the first provider. It is also essential 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 domain address being forwarded. One of the primary uses of a CNAME record is to direct a domain that you own through one provider to the servers of some other company assuming 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.