ironport.notifications.plateau.com has no MX records.
Question and response
Question
dig ironport.notifications.plateau.com. MX
Answer
The response has no answer records.
Authority
plateau.com. 3600 SOA ns1.sap.net. dns.sap-ag.de. 1772783560 3590 86400 2592000 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0