Microsoft is investigating an issue with its Microsoft 365 service and its Teams app, with some users reporting to DownDetector that they are having problems using services such as Exchange and Outlook.

On social media service X, Microsoft posted a message early Monday that it is assessing "an issue impacting users attempting to access Exchange Online or functionality within Microsoft Teams calendar." The problem appears to be affecting Microsoft users globally, according to posts from users.

"We've identified a recent change which we believe has resulted in impact. We've started to revert the change and are investigating what additional actions are required to mitigate the issue," Microsoft added in a subsequent post. 

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

University of Galway "is aware of an issue impacting some Microsoft 365 services, including Outlook, Outlook Calendars, Teams etc," noted the Irish university's IT group on X. "This is an intermittent issue impacting Microsoft 365 customers globally. Microsoft is aware & investigating."

Reports of outages began at about 4 a.m. Eastern time, according to DownDetector.

Monday's problems with Microsoft 365 comes after a massive outage in July, when banks, airlines, health systems and other industries that rely on the service were hit by a technical problem caused by global cybersecurity firm CrowdStrike. 

The disruption, which led to thousands of flights and train services being canceled globally, spawned a number lawsuits, with Delta Air Lines suing CrowdStrike and Microsoft over the outage, which took down the airline's internal systems and caused chaos for travelers.