As far as i know the cloudFlare forwards your traffic through their network by replacing the IP in DNS records with CloudFlare's IP. CloudFlare does not offer any service for forwarding mails and when you take a MX record and point it to a CloudFlare forwarded domain CloudFlare will give away server's real IP.
So a better practice is to use a third party mail service (e.g. Zoho, Google Apps, etc.) You can then point the MX record to the new record or mail server not located on your machine, and keep the real IP hidden safely.