mail.mesquiteweb.com has no CNAME records.
Question and response
Question
dig mail.mesquiteweb.com. NS
Answer
The response has no answer records.
Authority
mesquiteweb.com. 60 SOA ns1.systemdns.com. hostmaster.systemdns.com. 1739615425 604800 86400 300 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0