What's SPF

SPF (Sender Policy Framework)

Sender Policy Framework (SPF) is an email validation system designed to prevent email spam by detecting email spoofing, a common vulnerability, by verifying sender IP addresses. SPF allows administrators to specify which hosts are allowed to send mail from a given domain by creating a specific SPF record (or TXT record) in the Domain Name System (DNS). Mail exchangers use the DNS to check that mail from a given domain is being sent by a host sanctioned by that domain’s administrators.

If your email is send from the ip of your domain, then you don’t need set it at all.

You can use https://senderscore.org/ to test the score of your domain.