mail01.de.umantis.com has no CNAME records.
Question and response
Question
dig mail01.de.umantis.com. NS
Answer
The response has no answer records.
Authority
de.umantis.com. 773 SOA ns1.umantis.com. hostmaster.umantis.com. 2026021901 7200 1800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0