smtp.deliverabilitymanager.net has no MX records.
Question and response
Question
dig smtp.deliverabilitymanager.net. MX
Answer
The response has no answer records.
Authority
deliverabilitymanager.net. 300 SOA ns0.transip.net. hostmaster.transip.nl. 2026012603 86400 1800 2419200 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0