mx.fc-kalkofen.com has no CNAME records.
Question and response
Question
dig mx.fc-kalkofen.com. NS
Answer
The response has no answer records.
Authority
fc-kalkofen.com. 324 SOA dns.fc-kalkofen.com. hostmaster.fc-kalkofen.com. 1207327322 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0