You wish to host a mailserver on an EC2 instance. What two steps must you take to ensure utmost reliability?

A. Create an EIP for the instance.
B. Configure the mail service to serve as an open relay.
C. Contact AWS to have a Reverse DNS record configured and to help keep your domain from SPAM blacklists.
D. Provide open security group access to your instance on ports 25, 3389 and 22.