What happens with reverse DNS lookups and Amazon EC2?
Normally, if you perform a Reverse DNS Lookup on an EC2 instance with an Elastic IP, it will resolve to an AWS generated domain name.
For example: 220.127.116.11 resolves to "ec2-75-101-159-208.compute-1.amazonaws.com"
Top Level Domain: "amazonaws.com"
Country IP Address: UNITED STATES
So even though you have your DNS Made Easy settings set to www.yoursite.com to point to the EIP 18.104.22.168, when you do an nslookup, it returns the Amazon domain instead of yoursite.com.
In April 2010, Amazon introduced support for configuring reverse DNS (RDNS) records for your Elastic IPs, which will allow you to assign a static reverse DNS record to an Elastic IP.
To apply for RDNS, you must complete Amazon's Request to Remove Email Sending Limitations form.
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