M365 External Forwarding to Ticketing etc. Requires New Setting

Until recently, you could set up an inbox rule in Microsoft 365 (formerly Office 365) that would automatically forward emails e.g., to a ticketing system or to a cell phone. Sometime in the last few weeks, that stopped working. The bounced message includes this line:

550 5.7.520 Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance. AS(7555)

Turns out there is a special setting in the Exchange Online Protection that controls whether you are allowed to forward externally. Now that this is enforced, to allow automatic external forwarding, go to https://protection.office.com/antispam, edit the Outbound spam filter policy, and change  Automatic forwarding from “Automatic” to “On”.

Documentation:

https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/external-email-forwarding?view=o365-worldwide

Credit:

https://answers.microsoft.com/en-us/outlook_com/forum/oemail-osend/office-365-for-business-email-account-forwarding/d6de1ae5-ebfc-4031-abe3-a9b9de9b68a8