mail.atginternet.com has no CNAME records.
Question and response
Question
dig mail.atginternet.com. NS
Answer
The response has no answer records.
Authority
atginternet.com. 10687 SOA ns1.atginternet.com. hosting.atginternet.com. 2026010100 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0