Microsoft 365 Alert : Service Degradation – Exchange Online – Small number of users are blocked from sending email to external recipients – RESTORED

Announcements Aftab Alam

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.