relay-5.mail.level3.net has no CNAME records.
Question and response
Question
dig relay-5.mail.level3.net. NS
Answer
The response has no answer records.
Authority
Level3.net. 3600 SOA ns2.Level3.net. dns.level3.net. 2026030311 7200 600 2592000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0