SPF should written in TXT Record (not SPF Record)

SPF (Sender Policy Framework) should written in TXT record. It was considered to use SPF record (type 99). But, developers of SPF choose TXT record. So, you should write SPF in TXT record.

References

Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1 - 3.1.  DNS Resource Records

https://tools.ietf.org/html/rfc7208#section-3.1

SPF Record Deprecated

https://mxtoolbox.com/problem/spf/SPF-Record-Deprecated?page=health_spf&hidetoc=0&hidepitch=0&showlogin=1&action=spf:daum.net&domain=daum.net