o3.mailrelay.okta.com has no CNAME records.
Question and response
Question
dig o3.mailrelay.okta.com. NS
Answer
The response has no answer records.
Authority
okta.com. 60 SOA ns-1563.awsdns-03.co.uk. hostmaster.okta.com. 1664 3600 600 604800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0