Microsoft Exchange Online outage blocks access to mailboxes worldwide

Microsoft is investigating an ongoing outage blocking Exchange Online customers worldwide from accessing their mailboxes or sending/receiving emails.

Affected users see "550 5.4.1 Recipient address rejected: Access denied" errors when trying to send or when receiving messages, starting today at 1:11 PM UTC.

"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 tweeted earlier today.

Customers are also reporting on Twitter and Reddit that large percentages of emails sent to Exchange Online mailboxes will not reach the recipients' mailboxes.

"We've identified a potential Directory Based Edge Blocking (DBEB) issue that may be contributing to impact," Microsoft said in a service health alert issued today at 5:22 PM UTC.

"We're investigating this alongside our existing diagnostic data to determine our next steps. Impact is specific to users who are served through the affected infrastructure in North America, Europe, and the United Kingdom."

DBEB lets admins configure message rejection for invalid recipients and blocking for all messages sent to email addresses not present in Microsoft 365 or Office 365.

While Redmond said 30 minutes ago that telemetry data indicated that the service was starting to recover, a subsequent update says that additional monitoring revealed that the outage is still ongoing.

Earlier today, Redmond also mitigated a second outage preventing some users in the Asia Pacific region from accessing the Exchange Online and Microsoft Teams services.

Another worldwide outage took down multiple Microsoft 365 services in late January after a router IP address change led to packet forwarding issues between routers in Microsoft's Wide Area Network (WAN).

The list of services affected by last month's outage included Microsoft Teams, Exchange Online, Outlook, SharePoint Online, OneDrive, the Microsoft 365 Admin Center, Microsoft Graph, Microsoft Intune, and several Microsoft Defender products.

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Update March 01, 16:01 EST: Microsoft says the issue has been resolved by rerouting Exchange Online Protection (EOP) traffic away from the affected infrastructure.