January 25, 6:14am

Title: Users may be unable to access the Exchange Online service using Outlook on the web
User Impact: Users may be unable to access the Exchange Online service using Outlook on the web.
More info: This issue was previously communicated under MO502273 and has been created to highlight ongoing investigations into potential residual impact within the Exchange Online service.
Current status: Monitoring telemetry indicates that there is potential residual impact for a small number of users attempting to connect to the Exchange Online service using Outlook on the web after the resolution of the issue previously communicated under MO502273 was resolved. We're reviewing error messages and infrastructure diagnostics to determine the root cause and determine if this is an issue with the monitoring telemetry systems. In parallel, we're restarting applications on impacted mailbox infrastructure to provide relief if there is any user impact.
Scope of impact: This issue could potentially impact any user routed through the affected components.
Next update by: Wednesday, January 25, 2023, at 4:00 PM UTC

January 25, 7:40am

More info: This issue was previously communicated under MO502273 and has been created to highlight ongoing investigations into potential residual impact within the Exchange Online service.
Current status: Following our review of error messages and infrastructure diagnostics, we’ve established that residual impact from the issue previously communicated under MO502273 may be affecting some Exchange Online users. While we examine service telemetry to further understand the extent of the remaining issue, we’re removing specific affected sections of infrastructure from active rotation, while also restarting the associated shared cache and application pool to remediate impact.
Scope of impact: This issue could potentially impact any user routed through the affected components.
Next update by: Wednesday, January 25, 2023, at 6:00 PM UTC

January 25, 9:40am

More info: This issue was previously communicated under MO502273 and has been created to highlight ongoing investigations into potential residual impact within the Exchange Online service. 
Current status: We've confirmed that this issue is residual impact caused by a broadly impacting Azure networking issue previously communicated under MO502273, in which a specific subset of infrastructure was operating in a suboptimal state. This residual impact is being caused by excessive memory consumption correlated to shared cache on the impacted infrastructure. We’re running commands to isolate the affected infrastructure and are reviewing options to clear the shared cache to fully resolve the issue. 
Scope of impact: This issue could potentially impact any user routed through the affected infrastructure. 
Start time: Wednesday, January 25, 2023, at 7:05 AM UTC 
Root cause: Excessive memory consumption correlated to shared cache on specific infrastructure is resulting in impact. 
Next update by: Wednesday, January 25, 2023, at 8:00 PM UTC

January 25, 12:04pm

More info: This issue was previously communicated under MO502273 and has been created to highlight ongoing investigations into potential residual impact within the Exchange Online service. 
Current status: We’ve confirmed that our ongoing efforts to isolate the affected infrastructure, removing it from service, managing traffic on their shared cache to alleviate pressure, and then reinstating the infrastructure, is showing positive signs in availability for most affected users. We’re continuing to monitor, detect, and address individual problematic infrastructure to perform our mitigation and ensure that the issue resolves for all impacted users. 
Scope of impact: This issue could potentially impact any user routed through the affected infrastructure. 
Start time: Wednesday, January 25, 2023, at 7:05 AM UTC 
Root cause: Excessive memory consumption correlated to shared cache on specific infrastructure is resulting in impact. 
Next update by: Wednesday, January 25, 2023, at 10:00 PM UTC

January 25, 1:57pm

More info: This issue was previously communicated under MO502273 and has been created to highlight ongoing investigations into potential residual impact within the Exchange Online service.  
Current status: We've determined that this issue is largely resolved as a result of our previous remediation actions. We're still detecting some low-grade intermittent failures occurring in all affected regions, and we're isolating individual affected infrastructure and applying manual mitigations as they arise until we confirm that service is fully restored. 
Scope of impact: This issue could potentially impact any user routed through the affected infrastructure.  
Start time: Wednesday, January 25, 2023, at 7:05 AM UTC  
Root cause: Excessive memory consumption correlated to shared cache on specific infrastructure is resulting in impact.  
Next update by: Thursday, January 26, 2023, at 12:30 AM UTC

January 25, 3:36pm

More info: This issue was previously communicated under MO502273 and has been created to highlight ongoing investigations into potential residual impact within the Exchange Online service.
Current status: While we’ve determined that this issue is largely resolved by our previous mitigation actions, we're still detecting some low-grade intermittent failures occurring predominantly within the Germany-region. We're continuing the process of isolating individual affected infrastructure and applying manual mitigations until the service is fully restored.
Scope of impact: This issue could potentially impact any user routed through the affected infrastructure.
Start time: Wednesday, January 25, 2023, at 7:05 AM UTC
Root cause: Excessive memory consumption correlated to shared cache on specific infrastructure is resulting in impact.
Next update by: Thursday, January 26, 2023, at 9:00 AM UTC