mailer.corisvc.com has no CNAME records.
Question and response
Question
dig mailer.corisvc.com. NS
Answer
The response has no answer records.
Authority
corisvc.com. 600 SOA ns59.domaincontrol.com. dns.jomax.net. 2024080100 28800 7200 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0