mail.global.frontbridge.com has no CNAME records.
Question and response
Question
dig mail.global.frontbridge.com. NS
Answer
The response has no answer records.
Authority
global.frontbridge.com. 60 SOA ns1a.o365filtering.com. isgnoc.microsoft.com. 2023112101 10800 3600 604800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0