Sender Policy Framework or SPF is an email authentication protocol that protects domains from cyber attacks like spoofing, phishing and spam. It allows domain owners to specify which email servers are permitted to send emails from their domain(s). This way, it is able to detect emails sent by forged sender addresses.
Unfortunately, SPF has several built-in limits that many people are unaware of. It is no secret that properly implementing SPF is not an easy task to accomplish. Moreover, the SPF protocol is confined to detecting a forged sender claim in the email’s envelope, which is used when the email bounces back.
SPF’s most significant stumbling block is the domain lookup limit. If this limit is exceeded, emails will fail the SPF check even if they are authentic. Furthermore, SPF’s use of the Return-Path address, which is the primary method for mail servers to identify the source of an email irrespective of the human-readable ‘From’ address, creates a loophole that allows phishing attacks that authenticate correctly but have a forged ‘From’ address.