mx0b-005c1903.pphosted.com has no CNAME records.
Question and response
Question
dig mx0b-005c1903.pphosted.com. NS
Answer
The response has no answer records.
Authority
pphosted.com. 80 SOA ns1.proofpoint.com. ops.proofpoint.com. 2026070577 1200 120 2419200 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0