mx1.teledata-fn.de has no MX records.
Question and response
Question
dig mx1.teledata-fn.de. MX
Answer
The response has no answer records.
Authority
teledata-fn.de. 3600 SOA auth02.ns.td-fn.net. hostmaster.td-fn.net. 2026022301 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0