dns.theory7.nl has no MX records.
Question and response
Question
dig dns.theory7.nl. MX
Answer
The response has no answer records.
Authority
theory7.nl. 3600 SOA dns.theory7.nl. hostmaster.theory7.nl. 2024090601 10800 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0