External forwarding from Office 365 Exchange mailbox stops working
Emails forwarded to external addresses from MS Office 365 Exchange mailboxes no longer get forwarded. Instead, the following bounce message goes back to users' mailbox:
Delivery has failed to these recipients or groups:
Your message wasn't delivered because the recipient's email provider rejected it.
Diagnostic information for administrators:
Remote Server returned '550 5.7.520 Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance. AS(7555)'