mrelay4.amadeus.net has no MX records.
Question and response
Question
dig mrelay4.amadeus.net. MX
Answer
The response has no answer records.
Authority
amadeus.net. 600 SOA mucdns01.amadeus-dns.com. nicadmin.amadeus.com. 2008030525 3600 1200 2592000 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0