550 5.7.520: External forwarding is not allowed

Microsoft 365SMTP

The error usually looks like this:

550 5.7.520 Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance.

What it means

A forwarding rule tried to send email outside your organization, but Microsoft 365’s outbound spam policy blocks automatic external forwarding.

Common causes

  • Automatic forwarding to external addresses is disabled by default in Microsoft 365.

How to fix it

  1. An administrator can allow automatic forwarding for specific users in Microsoft Defender → Policies → Anti-spam → Outbound policy.

Tools to help diagnose it

Email header analyzer

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