smtp.bithal.de has no CNAME records.
Question and response
Question
dig smtp.bithal.de. NS
Answer
The response has no answer records.
Authority
bithal.de. 4641 SOA ns.kellerbu.de. sj.bithal.de. 2024051903 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0