mx.mccarthy4boston.com has no CNAME records.
Question and response
Question
dig mx.mccarthy4boston.com. NS
Answer
The response has no answer records.
Authority
mccarthy4boston.com. 3444 SOA dns.mccarthy4boston.com. hostmaster.mccarthy4boston.com. 1681414331 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0