mailx.nitro.org has no CNAME records.
Question and response
Question
dig mailx.nitro.org. NS
Answer
The response has no answer records.
Authority
nitro.org. 2335 SOA ns1.nitro.org. kjoostens.gmail.com. 2023101901 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0