SPF (Sender Policy Framework) is a DNS record that was wrote a global IP address of mail server. The server that received the mail tries to get the SPF record from the domain name of the address written in From, and check the source IP address.

reference

@ SPF "v=spf1 +ip4:219.117.***.***/32 +ip4:219.117.***.***/32 ~all"
@ TXT "v=spf1 +ip4:219.117.***.***/32 +ip4:219.117.***.***/32 ~all"

I will also write a TXT record. You can only write one SPF record.

Yahoo Mail makes it easy to find out if you've successfully passed your SPF.