ipv4.wtnet.de has no MX records.
Question and response
Question
dig ipv4.wtnet.de. MX
Answer
The response has no answer records.
Authority
ipv4.wtnet.de. 300 SOA dns4.wtnet.de. hostmaster.wtnet.de. 2026030603 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0