I receive the error code 550 5.7.x in Exchange Online after I sent an email message:
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)'
I am experiencing issues with inbound mail due to Microsoft disabling automatic forwarding to external addresses in Office 365. What can I do?
If your Zendesk Support account is using mail forwarding from Microsoft email addresses, your Zendesk Support addresses may be disabled as a result. Disabling automatic forwarding to external addresses in Office 365 is being rolled out in phases with details communicated by Microsoft via Message Center posts.
To learn more about email forwarding in Microsoft 365, see the article: Control automatic external email forwarding in Microsoft 365.
To resolve this issue, work with your IT email administrator to make the changes required by Microsoft, as outlined in the article: Fix email delivery issues for error code 550 5.7.1 in Exchange online.