mailserver1.viaginterkom.de has no CNAME records.
Question and response
Question
dig mailserver1.viaginterkom.de. NS
Answer
The response has no answer records.
Authority
viaginterkom.de. 6209 SOA ns1.o2online.de. hostmaster.o2online.de. 2026010200 14400 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0