smtp.crossflowcloud.com has no CNAME records.
Question and response
Question
dig smtp.crossflowcloud.com. NS
Answer
The response has no answer records.
Authority
crossflowcloud.com. 3559 SOA dns2.wavify.com. root.crossflowcloud.com. 2024102200 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0