box.rezmail.net has no CNAME records.
Question and response
Question
dig box.rezmail.net. NS
Answer
The response has no answer records.
Authority
rezmail.net. 10800 SOA ns03.red-spectrum.com. hostmaster.box.rezmail.net. 2022012400 7200 86400 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0