Microsoft is investigating yet another worldwide outage, this time affecting Exchange Online, its cloud-based email service. The problems reportedly began around 1 PM UTC (7 AM ET).

The Microsoft 365 Status Twitter feed states: “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.”

The thread continues, “Users are reporting receiving an error including “550 5.4.1 Recipient address rejected: Access denied” and we are investigating further.”

Bleeping Computer reports that Microsoft issued a service health alert at 5:22 PM UTC saying it had identified a potential Directory Based Edge Blocking (DBEB) issue, and is investigating further. DBEB allows administrators to reject messages sent to invalid recipients in Exchange Online.

The company said that “impact is specific to users who are served through the affected infrastructure in North America, Europe, and the United Kingdom.”

As of approximately 3 PM ET, Microsoft tweeted that it is now routing traffic away from what appears to be the affected infrastructure as a potential mitigation strategy.

Update: As of 4 PM ET, Microsoft 365 Status tweeted: “We’ve confirmed that rerouting EOP traffic to alternate infrastructure has resolved the user impact.”

We will update this story as more information becomes available.

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