mx4.lew.de has no CNAME records.
Question and response
Question
dig mx4.lew.de. NS
Answer
The response has no answer records.
Authority
lew.de. 10785 SOA ns1.lewtelnet.de. hostmaster.lewtelnet.de. 2026022706 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0