ODM: Email Forwarding blocked by tenant policy (4241815)

The default Anti-spam outbound policy under the Microsoft Security Center may be configured to block email forwarding. 

This may be the default behavior for the following:

• Microsoft Office 365 Demo Tenants
• Tenants with less than 300 users (small business tenants)

The policies controlling whether forwarding is enabled or disabled within an Office 365 tenant are controlled by Microsoft 365 Defender.

• Logon to the Microsoft Security admin center
• Click Policies and rules
• Click Threat policies
• Click Anti-spam policies

From here there is the ability create a policy.  The policy can be scoped to the users or groups to enable forwarding.