fra-out-015.esa.eu-central-1.outbound.mail-perimeter.amazon.com has no CNAME records.
Question and response
Question
dig fra-out-015.esa.eu-central-1.outbound.mail-perimeter.amazon.com. NS
Answer
The response has no answer records.
Authority
eu-central-1.outbound.mail-perimeter.amazon.com. 190 SOA ns-258.awsdns-32.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0