mail.Chartercom.com has no CNAME records.
Question and response
Question
dig mail.Chartercom.com. NS
Answer
The response has no answer records.
Authority
Chartercom.com. 2178 SOA ns1.charter.com. hostmaster.charter.com. 2025060157 43200 3600 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0