_spf.s1004.mx.srv.dfn.de has no MX records.
Question and response
Question
dig _spf.s1004.mx.srv.dfn.de. MX
Answer
The response has no answer records.
Authority
dfn.de. 3600 SOA ns1.dfn.de. hostmaster.dfn.de. 1771951111 28800 7200 3024000 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0