This tutorial covers the steps you should take if, when you change your domain to point to Cloudflare, you no longer receive emails to your domain
1. Do you have any MX records set for your domain?
You will need to have MX records set in the DNS tab of your Cloudflare dashboard for you to receive emails. There is also a tutorial on Adding DNS Records if you need help with this.
2. Is the name field of your MX record set to @?
If not, it covers a subdomain for mail, not the mail domain. Make sure the name is set to @ or yourdomain.com
3. Do your MX records point to mail.yourdomain.com (or similar)?
If so, make sure you have an A record set for mail pointing to the IP address of the server that handles your mail (given by your email provider or web host). (make sure this is set to )
4. Do you have an A record (normally mail) pointing to the IP of the server where your mail is hosted?
If so, make sure that the A record is set to , NOT .