Inline Email Security and Microsoft 365: A Practical View of Mail Routing, Risk, and Prevention

Microsoft’s guidance on inbound and outbound mail routing for third-party email security has prompted a fair question from customers: how should organizations evaluate inline email security for Microsoft 365? The answer depends less on whether a solution is inline and more on how that inline architecture is implemented. Microsoft is right to call attention to mail flow designs that can introduce unnecessary complexity, create authentication challenges, duplicate processing, or disrupt the expected Microsoft 365 experience.