Sender Policy Framework (SPF) helps to fight against email spoofing for your organization. SPF is generally a TXT record in DNS Zone file that lists the host name or IP address authorized for sending emails for a specific domain name. There is no other configuration required however the recipients must have SPF checking enabled as part of anti-spam protection suite.
For an example, TXT record for the domain – itadminguide.com would be as follows.
spf1 means SPF version 1
ip4:x.x.x.x means IPV4 host.
-all means ‘all other hosts’ are not allowed to send. REJECTED.
Read SPF Syntax – http://www.openspf.org/SPF_Record_Syntax
Test your SPF – https://mxtoolbox.com/spf.aspx