Post-delivery protection is a security control that continues inspecting a message after it has already reached the user. Instead of stopping only at the gateway, it can later warn the recipient, quarantine the message, remove it from a mailbox or chat, or trigger remediation when new threat intelligence arrives.
This matters because modern phishing often evades first-pass filters, especially when the payload is hidden in attachments, shortened URLs, images, or QR codes. Post-delivery protection helps close that gap by turning a missed threat into a managed event. In practice, defenders use it to add banners, block clicks, retract malicious messages, and generate telemetry for investigation. In collaboration tools like Teams, it can surface warnings after delivery so analysts and users still get a chance to respond before the message leads to credential theft or malware.