SPF (Sender Policy Framework) and DMARC (Domain-based Message Authentication, Reporting, and Conformance) are email authentication controls that help receivers check whether a message really comes from a domain it claims to use. SPF validates whether the sending server is authorized for that domain, while DMARC adds policy and alignment rules so the visible “From” address matches authenticated domain data.
These controls matter because spoofed email is a common starting point for phishing and business email compromise. When SPF and DMARC pass, mail systems can trust the sender signal more strongly; when they fail, defenders may quarantine, reject, or flag the message. In attacks using calendar invites or other attachments, these checks can still help expose forged senders, but they do not inspect the contents of an .ics file or the links inside it. For that reason, SPF and DMARC are valuable layers, not a complete defense against social engineering.