How to Create a PTR Record for AWS Mailserver's Elastic IP Address

I configured an SMTP server (Postfix) on an AWS instance. However, as a defense against spam most well-managed emailservers will reject messages ***sent*** from any host whose IP does not resolve back to the same hostname of the sending server. When I sent a test message from the CLI: mail -s 'TEST Subject' addressOfRecpient@test.com <<< 'Test Message Sent from Postfix Server' It gets rejected by the recipient's mailserver. ***How do I create a PTR record for the Elastic IP assigned to my AWS mailserver?***