ID-02HighRecommended Secure

Block Legacy Authentication

Identity & Authentication control for Microsoft 365 and Entra ID

Why This Control Matters

Legacy protocols like IMAP and POP3 cannot enforce MFA. Attackers specifically target these protocols to bypass your MFA policies. Blocking them closes a major attack vector.

Expected State

When this control is compliant, your tenant should meet these criteria:

1A Conditional Access policy blocks legacy authentication protocols (IMAP, POP3, SMTP, older Office clients)
2No exceptions for legacy protocols except documented service accounts

Enforcement

Default Mode

Advisory

Alerts on deviations but does not make changes

Auto-Remediation

Available

Creates a Conditional Access policy blocking legacy authentication for all users

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