mail.priotas.com has no CNAME records.
Question and response
Question
dig mail.priotas.com. NS
Answer
The response has no answer records.
Authority
priotas.com. 3504 SOA rc78.3uu.net. hostmaster.3uu.net.priotas.com. 2025123111 3600 3600 3600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0