16/12/2021 07:41:00 AM (GMT)
Issue Reported : 15/12/2021 09:47:00 AM (UTC)
Microsoft Reference : EX305510
Issue Status: RESTORED
Issue Description: Users are blocked from sending email to external recipients.
More info: Admins were experiencing delays in unblocking the users, which were previously blocked by Microsoft 365 Defender.
Affected users may have received the error message: ‘550 5.1.8 Access denied, bad outbound sender AS(42003)’.
Users could send email to users within their organization as expected.
Scope of impact: A small number of users that were previously blocked by Microsoft 365 Defender and were routed through the affected infrastructure may have been affected.
Final Update – 16/12/2021 05:00:00 PM: Microsoft completed the deployment of a fix to prevent this impact from occurring to additional users as well as unblocking all remaining mailboxes.