Access Issues for Microsoft Exchange Online Mailboxes

On March 1, 2023, at ~11:56 AM EST, Microsoft communicated via tweet (@MSFT365status) that they were investigating an issue in which users were unable to access Microsoft Exchange Online mailboxes.

Microsoft provided service incident number EX52202 for system admins to refence in the Microsoft Admin Center.

We're investigating an issue wherein users may be unable to access their Exchange Online mailboxes via any connection method. Additional details can be found within the Service Health Dashboard under EX522020.

— Microsoft 365 Status (@MSFT365Status) March 1, 2023

Earlier in the day, Microsoft also reported a service incident, MO521925, which impacted the APAC region and involved users unable to access some Exchange Online services and Microsoft Teams.

As to the new service incident EX522020, Microsoft then communicated via tweet additional details as to mailbox access issue, namely the error message users were receiving: "550 5.4.1 Recipient address rejected: Access denied,"  However Microsoft's investigation was ongoing and no fix was announced at this time.

Users are reporting receiving an error including "550 5.4.1 Recipient address rejected: Access denied" and we are investigating further. More details can be found in the admin center under EX522020.

— Microsoft 365 Status (@MSFT365Status) March 1, 2023

At approximately 1:30 PM EST, about 90 minutes from their first message as to this service incident, Microsoft was indicating a recovery of services for most of the impacted areas.  But it should be noted that at this time Microsoft had still not identified a cause.

Our telemetry indicates that the service has largely recovered. We're continuing to investigate to determine the root cause and whether additional action is required. More detail can be found under EX522020 in the admin center.

— Microsoft 365 Status (@MSFT365Status) March 1, 2023

A follow-up tweet just 20 minutes later had Microsoft back pedaling a bit, as the original mailbox access issues persisted.  Microsoft was now confirming that their investigation, and efforts to remediate, were continuing at this time.

Our continued monitoring has indicated that the issue is ongoing. We’re continuing to investigate, and more detail can be found under EX522020 in the admin center.

— Microsoft 365 Status (@MSFT365Status) March 1, 2023

By 3:00 PM EST, Microsoft was communicating that some remediation efforts were in place.  Microsoft was at this time routing Exchange Online Protection (EOP) traffic away from impacted infrastructure.  Once completed with their rerouting of the EOP traffic, Microsoft then would reach out to affected users to begin confirming resolution.

We're in the process of routing EOP traffic away from what appears to be the affected infrastructure as a potential mitigation strategy. More details can be found in the admin center under EX522020.

— Microsoft 365 Status (@MSFT365Status) March 1, 2023

Many Twitter responses from the community at this time were still confirming that the bounces and related mailbox access issues continued.

But by 4:00 PM EST, Microsoft communicated that the issue was resolved.

We've confirmed that rerouting EOP traffic to alternate infrastructure has resolved the user impact. More details can be found in the admin center under EX522020.

— Microsoft 365 Status (@MSFT365Status) March 1, 2023

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