Microsoft is working to resolve an ongoing Exchange Online outage affecting customers throughout North America, blocking their access to emails.

“We’re investigating an issue affecting a portion of infrastructure in North America, where users may be unable to access their mailbox via any Exchange Online connection method,” the company explained earlier today.

According to user reports on DownDetector, the issue began impacting Microsoft’s customers more than six hours ago and is causing server connection problems, affecting users who attempt to log in to their accounts and access Teams, Outlook, and Hotmail.

While the root cause has yet to be determined and Microsoft hasn’t shared the number of customers affected by this outage, the company said that it’s currently investigating telemetry data and working to mitigate the impacted infrastructure.

“We’re continuing to evaluate service telemetry for potential system irregularities contributing to impact, and in parallel we’re applying some changes to optimize affected mailbox infrastructure,” Microsoft added in a recent update.

Earlier this week, Redmond resolved another issue that caused an anti-spam service to quarantine some emails and mistakenly block Exchange Online and Microsoft Teams users from opening URLs.

The company is also rolling out a fix to address an Exchange Online issue that triggers email access problems for Outlook mobile users who use Hybrid Modern Authentication (HMA).

The issue began impacting Android and iOS users on August 17, causing mailboxes to crash and preventing them from accessing their email and calendars.

Update September 11, 18:12 EDT: According to an admin center update, the outage also impacts customers in South America. Microsoft says it’s seeing signs of recovery after implementing a configuration change to some of the impacted infrastructure.

“We’ve seen some steady improvements in service quality as our manual database optimizations and configuration changes have reduced the impact of the high service utilization on the environment,” the compay notes.

“Additionally, we’re looking into a potential build versioning issue with a subset of machines supporting the service that may be contributing to impact.”

This is a developing story…