smtp.lis-ag.de has no CNAME records.
Question and response
Question
dig smtp.lis-ag.de. NS
Answer
The response has no answer records.
Authority
lis-ag.de. 10800 SOA rz-ns-01.winsped.de. administrator.lis.eu. 2011112501 21600 21600 864000 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0