Why am I getting an SOA email error when I check my DNS?

Delivery over IPv4 to awsdns-hostmaster@amazon.com could not be done and Failed to deliver email for SOA RNAME of mydomain.com (awsdns-hostmaster.amazon.com) using awsdns-hostmaster@amazon.com are errors often seen when user check DNS with http://dnscheck.pingdom.com/. Pingdom is using an old version of .SE's DNSCheck tool that often gives false positives and false negatives. Read more about that here: https://forums.aws.amazon.com/thread.jspa?messageID=440455