SPF (Sender Policy Framework) is an email authentication protocol that helps inboxes filter out unwanted emails by verifying the sender's domain. It declares a list of allowed origins, and if an email doesn't match, it's considered spam. A domain or subdomain can only have one SPF policy, which is usually set in a TXT record. Inboxes look at the Return-Path to confirm the message's legitimacy. Once passed, a vetting process begins with DKIM (DomainKeys Identified Mail), which adds a signature to verify the email sender's identity using a private/public key pairing. If an email fails SPF or DKIM, DMARC (Domain-based Message Authentication, Reporting & Conformance) sets rules for handling such cases, and implementing it enhances a domain's reputation by preventing suspicious messages from being delivered. BIMI (Brand Indicators for Message Identification) is another way to stand out in the inbox by showcasing a brand's legitimacy through logo display and verified checkmarks, but obtaining it requires an exclusive verification process.