mail01.ossds.com has no CNAME records.
Question and response
Question
dig mail01.ossds.com. NS
Answer
The response has no answer records.
Authority
ossds.com. 300 SOA ns1.ossds.com. noc.ossds.com. 2026022300 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0