_spfblockb.navercorp.com has no CNAME records.
Question and response
Question
dig _spfblockb.navercorp.com. NS
Answer
The response has no answer records.
Authority
navercorp.com. 36 SOA ns1.naver.com. webmaster.navercorp.com. 2026022607 21600 1800 1209600 180
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0