The email address you want to send mail from. It can be any address you want, as long as it ends with @<your domain name>. You can use info@<your domain>, contact@<your domain>, your.name@<your domain>, or anything else.
You may want to choose an address you’ve set up to receive email with though. You can do the email receiving with any provider of your choice, and the author of this guide has written a guide to receive email with Cloudflare.