mail.onagap.com has no CNAME records.
Question and response
Question
dig mail.onagap.com. NS
Answer
The response has no answer records.
Authority
onagap.com. 32 SOA ns3.systemlifeline.com. alltechs.systemlifeline.com. 2026011801 3600 1800 1209600 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0