mxout01hhb.1und1.net has no CNAME records.
Question and response
Question
dig mxout01hhb.1und1.net. NS
Answer
The response has no answer records.
Authority
1und1.net. 2616 SOA dnsdb.versatel.de. hostmaster.versatel.de. 2026030513 21600 3600 604800 8640
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0