Zendesk recently became aware of some customers experiencing issues with inbound mail due to Microsoft disabling automatic forwarding to external addresses in Office 365.
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.
Who is Impacted
Impacted Zendesk users would receive the following error code 550 5.7.x in Exchange Online after sending 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)'
What you can do
In order to resolve this issue, please work with your IT email administrator to make the required changes Microsoft recommends outlined below.
You can read more about the change here: https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/external-email-forwarding?view=o365-worldwide
You can read about how to fix the error here: https://docs.microsoft.com/en-us/exchange/mail-flow-best-practices/non-delivery-reports-in-exchange-online/fix-error-code-550-5-7-1-in-exchange-online