dns-us.st has no MX records.
Question and response
Question
dig dns-us.st. MX
Answer
The response has no answer records.
Authority
dns-us.st. 3600 SOA ns.bahnhof.net. hostmaster.bahnhof.net. 2022112800 1800 600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0