mail.nitro.org has no CNAME records.
Question and response
Question
dig mail.nitro.org. NS
Answer
The response has no answer records.
Authority
nitro.org. 1014 SOA ns1.nitro.org. kjoostens.gmail.com. 2023101901 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0