ns4.sophos.com has no CNAME records.
Question and response
Question
dig ns4.sophos.com. NS
Answer
The response has no answer records.
Authority
sophos.com. 300 SOA asia1.akam.net. hostmaster.sophos.com. 2020012655 7200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0