Unitel recently became aware of some customers reporting they are not receiving notification emails for their Voicemail, Fax, or Billing. We have found that this complaint is isolated to customers using Microsoft Office 365.
Although our customers have not made configuration changes directly to their spam/junk settings, Microsoft has taken action to disable (by default) automatic forwarding to external addresses in Office 365.
If your email address uses mail forwarding from a Microsoft-hosted email service, your 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 users will 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.