SPF, the Sender Policy Framework, was the first protocol designed for an email sender to authorize their messages.
SMTP, Simple Mail Transfer Protocol, emphasized on reliability instead of security. This protocol is used for email communication over the internet with no way to verify where the email originated from.
SPF is a simple DNS TXT record that helps email admins to define what IP Addresses are authorized to send an email on behalf of their domain.
The receiving mail server performs a DNS query on the email Domain to look up the SPF record and match the IP addresses authorized with the origination IP Address of the email. If they match, the email goes in the inbox. If they don’t, the email gets marked as spam.
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