What is "legacy authentication" and why should you block it?

Legacy (basic) authentication is an older way apps sign in that doesn't support MFA, and it's one of the most common paths attackers use to break into mailboxes. Modern Outlook, Teams and mobile apps don't need it, so blocking it via Conditional Access or Exchange Online settings closes a door most businesses don't realise is open.

Coach's tip: check your sign-in logs for legacy auth attempts before you block it, so you catch any old device or app that still needs updating first.