Exchange Online Hardening · Microsoft 365 Security Checkliste

Skillplan M365 Checklist

2026-07-20 00:26

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Disable SMTP AUTH, IMAP, and POP at the tenant level; allow per-mailbox only with documented justification.

Disable automatic forwarding to external recipients via the Anti-spam outbound policy.

Verify mailbox audit logging is enabled for every mailbox.

Configure DKIM signing for every accepted domain; publish a strict DMARC p=reject after a monitoring period.

Enable the Anti-phishing policy with mailbox intelligence and impersonation protection for executives and high-value users.

Apply the External sender warning tag to all inbound mail from outside the organization.

Disable user-created Exchange Online mailbox auto-forwarding rules to external addresses.

Restrict the Mail Recipient Creation management role to a small named group; review quarterly.