Why Email Verifiers Can't Validate Microsoft 365—But Won't Admit It

Email verification tools are failing to detect Microsoft 365/Outlook mailboxes reliably, yet major vendors mislead users by returning false positives rather than acknowledging the limitation. Microsoft's intentional security design—refusing to validate recipient existence at the SMTP layer—has broken the industry-standard verification protocol that all email verification services depend on. For cold email operators and sales teams relying on high-confidence contact lists, this represents a critical infrastructure gap disguised as a product feature.