mail.1blu.de has no MX records.
Question and response
Question
dig mail.1blu.de. MX
Answer
The response has no answer records.
Authority
1blu.de. 180 SOA ns1.1blu-dns.de. hostmaster.1blu.de. 2026022001 14400 3600 604800 180
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0