mail0501.teamviewer.com has no CNAME records.
Question and response
Question
dig mail0501.teamviewer.com. NS
Answer
The response has no answer records.
Authority
teamviewer.com. 8956 SOA tv-ns1.teamviewer.com. hostmaster.teamviewer.com. 2017086251 43200 3600 2419200 86460
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0