When testing the SOA setting for example-domain.org on http://mxtoolbox.com/, it says that
SOA Serial Number Format is Invalid
The entry is
ns-885.awsdns-46.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
That, however, is exactly what Amazon suggest in their Route 53 documentation on http://docs.aws.amazon.com/Route53/latest/DeveloperGuide/SOA-NSrecords.html
mxtoolbox issues a warning - why? They also consider the missing DMARC settings as an error.
Please bear with me - I am not a sysadmin. Any hint that uses a language that a developer can understand is greatly appreciated.