You may need to reverse the host name from the global IP address to prove the legitimacy of the host.
Normally, if you are using a fixed IP, you need to have the owner of the IP address (provider, etc.) delegate the authority. If you are using Elastic IP, the IP address is managed. Since it is Amazon, I investigated the procedure
Thing you want to do
If you reverse-lookup an Elastic IP that is not set for reverse lookup, the host name automatically assigned to the instance will be returned as shown below.
Change this result to be your own domain.
Apply using the form below
Simply enter your application in each field and click Submit
Use Case Description
Enter the purpose of use. For
mail server operation, you should enter the purpose such as etc.
Elastic IP Address
Enter the Elastic IP you want to allow reverse lookup
Reverse DNS Record for EIP
Enter the domain name you want to set as a result of the reverse lookup
When the setting is completed, you will be contacted by e-mail within an hour. After that, it is OK if you can confirm that it is reflected by commands such as dig, nslookup etc.
More info we can find in link below: