How do I send reliable email from EC2?

Although Elastic IPs do help the reliability of sending mail from EC2, there is no way to pass a reverse DNS lookup on email originating from an EC2 instance.

If you want a high-reliability email solution on EC2, your best option is to relay your email through a third party forwarding service such as authsmtp, easydns, or dnsmadeeasy.

You could also relay your mail through your own proxy server outside of EC2, but unless you have extra unused machines and some free time, it is recommended that you use one of the third party email services.