staging.heysender.com has no MX records.
Question and response
Question
dig staging.heysender.com. MX
Answer
The response has no answer records.
Authority
heysender.com. 300 SOA ns1.curanet.dk. hostmaster.curanet.dk. 2025111401 14400 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0