smtp.cgrx.de has no CNAME records.
Question and response
Question
dig smtp.cgrx.de. NS
Answer
The response has no answer records.
Authority
cgrx.de. 3494 SOA ns1.asok.de. hostmaster.asok.de. 1772242754 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0