Microsoft 365 is experiencing an error. Here’s what you need to know.

Microsoft is investigating an issue with its Microsoft 365 service and its Teams app that some users are reporting Down detector that they have problems using services such as Exchange and Outlook.

On the social media service X, Microsoft posted a message early Monday that it is assessing “an issue affecting users trying to access Exchange Online or Microsoft Teams calendar functionality.” The issue appears to be affecting Microsoft users globally, according to user posts.

“We have identified a recent change that we believe resulted in impact. We have begun to reverse the change and are investigating what additional actions are required to address the issue,” Microsoft added in a subsequent post.

Microsoft 365 is a subscription-based app that bundles services like Word and Excel while providing cloud-based storage, while Teams is primarily used by workplaces for video calling and online chat. Although DownDetector, an online service that tracks technical outages, had only a few dozen reports of problems with 365 on Monday morning, users posted on social media that they were having problems with Microsoft services.

The University of Galway “is aware of an issue affecting some Microsoft 365 services, including Outlook, Outlook Calendars, Teams, etc. noticed the Irish University IT Group on X. “This is a recurring issue affecting Microsoft 365 customers globally. Microsoft is aware and investigating.”

Reports of outages began around 4 a.m. ET, according to DownDetector.

Monday’s problems with Microsoft 365 come after one massive fallout in Julywhen banks, airlines, healthcare systems and other industries that rely on the service were hit by a technical problem caused by global cyber security firm CrowdStrike.

The outage, which led to the cancellation of thousands of flight and train services globally, spawned a series of lawsuits with Delta Air Lines sue CrowdStrike and Microsoft over the outage, which took down the airline’s internal systems and caused chaos for travellers.