Outage in Microsoft 365
Some users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail
Resolved Minor
October 08, 2026 - Started 1 day ago
- Lasted about 4 hours
Incident Report
Summary AI Generated
Email messages sent from on-premises Exchange servers to Exchange Online intermittently failed over a 4.1-hour period, with affected users receiving the error "Mail sent to the wrong Office 365 region. ATTR35." Microsoft identified a service-side testing process as the likely root cause and was developing a remediation plan to restore service.
Title: Some users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail
User impact: Users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail.
Current status: We're investigating a potential issue with Exchange Online and checking for impact to your organization. We'll provide an update within 30 minutes.
User impact: Users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail.
Current status: We're investigating a potential issue with Exchange Online and checking for impact to your organization. We'll provide an update within 30 minutes.
Components affected
Exchange OnlineTrusted by 1,000+ teams
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Latest Updates ( sorted recent to last )
1 day ago - at 10/08/2026 04:20PM
Title: Some users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail
User impact: Users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail.
More info: Impacted users receive the following error "Mail sent to the wrong Office 365 region. ATTR35."
Current status: We've identified a potential root cause related to a service-side testing process. We're working on a remediation plan to correct this issue and restore service. This information may be updated as our investigation continues.
Scope of impact: Some users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail.
Next update by: Thursday, October 8, 2026, at 6:30 PM UTC
1 day ago - at 10/08/2026 03:14PM
Title: Some users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail
User impact: Users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail.
Current status: We're reviewing the information provided by some reporting users to better understand this issue and determine our next troubleshooting steps.
Scope of impact: Some users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail.
Next update by: Thursday, October 8, 2026, at 4:30 PM UTC
1 day ago - at 10/08/2026 02:53PM
Title: Some users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail
User impact: Users' email messages from on-premises Exchange servers to Exchange Online may intermittently fail.
Current status: We're investigating a potential issue with Exchange Online and checking for impact to your organization. We'll provide an update within 30 minutes.
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