mail-filter.afoyi.com has no CNAME records.
Question and response
Question
dig mail-filter.afoyi.com. NS
Answer
The response has no answer records.
Authority
afoyi.com. 1524 SOA ns1.afoyi.com. root.afoyi.com. 1772546726 10800 900 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0