Security Policy Errors

Fix Exchange Rule Forwards Internally but Not Externally

Olivia Miller Oct 10, 2026 870 views

Question details

The user needs to configure an Exchange mail flow rule to successfully perform automatic email forwarding to external email addresses.

How to Fix Exchange Rule Forwarding Internally But Not Externally

Product: Microsoft Exchange
Device & OS: not provided
Scenario: Setting up a mail flow rule to automatically redirect or forward inbound emails to external addresses.
Observed behavior: The Exchange rule successfully redirects messages to internal recipients, but fails or prevents automatic forwarding to external email addresses.

Before you start

Ensure you have Exchange Administrator or Global Administrator privileges in your Microsoft 365 tenant to access and modify outbound spam filtering policies.

Solution 1Recommended

Enable External Forwarding in Outbound Spam Filter Policies

Microsoft 365 disables automatic external forwarding by default for security purposes. You must explicitly allow it in your outbound anti-spam policy.

To protect against compromised accounts, Microsoft 365 enforces a default outbound spam policy that drops messages automatically forwarded to external recipients. Updating this policy is the most common fix for external forwarding failures.

Access Microsoft 365 Defender

Open Threat Policies

Click on 'Threat policies', then select 'Anti-spam' under the Policies section.

Edit the Outbound Policy

Click on 'Anti-spam outbound policy (default)' to open the properties panel, then click 'Edit protection settings' at the bottom.

Modify Forwarding Rules

Locate the 'Automatic forwarding rules' section. Change the dropdown setting from 'Automatic - System-controlled' to 'On - Forwarding is enabled'.

Save Changes

Click 'Save' to apply the new policy. It may take some time for the updated policy to propagate across your tenant.

Enable External Forwarding in Outbound Spam Filter Policies

Propagation Time: Changes to anti-spam policies can occasionally take up to 24 hours to fully take effect across all Microsoft 365 servers.

Solution 2

Run an Extended Message Trace

If updating the spam policy does not resolve the issue, a message trace will pinpoint the exact rule or policy dropping the external email.

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Frequently Asked Questions

Why does Microsoft 365 block external forwarding by default?

Microsoft disables automatic external forwarding by default to prevent data exfiltration and protect your organization's reputation in case a user's account is compromised and attempts to mass-forward spam.

Can I allow external forwarding for specific users only?

Yes. Instead of editing the default outbound spam policy, you can create a custom outbound anti-spam policy, set the forwarding rule to 'On', and assign that policy only to specific users or Microsoft 365 groups.

Will a mailbox inbox rule override the tenant's outbound spam policy?

No. Tenant-level security policies, such as the outbound spam filter policy, take precedence over both admin-created mail flow rules and user-created Outlook inbox rules.

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