mail.lewtelnet.de has no CNAME records.
Question and response
Question
dig mail.lewtelnet.de. NS
Answer
The response has no answer records.
Authority
lewtelnet.de. 1090 SOA ns1.lewtelnet.de. hostmaster.lewtelnet.de. 2026030118 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0