Microsoft 365 Alert – Service Degradation – Exchange Online – Users may be unable to access their Exchange Online mailbox or send/receive messages – RESOLVED

02/03/2023 09:15:00 AM (GMT)

NHSmail Reference : INC34568175

Microsoft Reference : EX522020

Issue Status : RESOLVED

Issue Description : Users may have been unable to access their Exchange Online mailboxes or send and receive email messages.

More Information : Users may have received an error message including: “550 5.4.1 Recipient address rejected: Access denied” when attempting to send or receive messages.

Final Update : 02/03/2023 09:15:00 AM – Microsoft have confirmed that rerouting EOP traffic away from the affected portion of infrastructure has successfully resolved the user impact.

Scope of impact : Impact was specific to users who are served through the affected infrastructure in North America, Europe, and the United Kingdom.

Root cause : A portion of Exchange Online Protection (EOP) infrastructure wasn’t operating as expected due to a potential misconfiguration, resulting in the impact.

Next steps : Microsoft are continuing to investigate the underlying cause of the issue. They are reviewing their telemetry signals to find ways to identify and resolve similar issues in the future more quickly.

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