Exchange Online Email delivery Needs an admin

550 5.7.520: your organization doesn't allow external forwarding

Likely causes

• A user's Inbox rule forwards mail to an external address.
• Mailbox (SMTP) forwarding to an external address is set on the mailbox.
• Automatic forwarding in the outbound spam policy is Off, or Automatic (which now means Off for most tenants).
• The forwarding rule was created by an attacker on a compromised account.

How to fix it

1. Find the forwarding: check the user’s Inbox rules and the mailbox’s forwarding setting. The Auto forwarded messages report in the Exchange admin center lists users who forward externally.
2. If nobody knows why the forward exists, treat the account as compromised: reset the password, revoke sessions, and remove the rule.
3. If the forward is legitimate and approved by your security policy, an admin creates a custom outbound spam filter policy with automatic forwarding set to On – Forwarding is enabled and applies it only to the users who need it.
4. Leave the default policy set to Off. Don’t turn forwarding on for everyone to fix one user.

Checked against: learn.microsoft.com, learn.microsoft.com