mx6.blazing.de has no CNAME records.
Question and response
Question
dig mx6.blazing.de. NS
Answer
The response has no answer records.
Authority
blazing.de. 673 SOA ns1.blazing.de. tspier.blazing.de. 2013040433 14400 3600 604800 38400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0