STORY: Microsoft Teams and Outlook were hit by network outages on Wednesday (January 25).
The U.S. tech giant did not say exactly how many users were affected.
But data from the outage tracking website Downdetector showed almost 4,000 incidents in India.
900 were spotted in Japan.
Outage reports also spiked in Australia, Britain and the UAE.
Microsoft said it was investigating a networking issue.
Users found they could not exchange messages, join calls or use any features of the Teams app.
Many shared updates about the issue on Twitter and #MicrosoftTeams trended as a hashtag on the social media site.
Teams is used by more than 280 million people.
It forms a key part of daily operations for many businesses and schools.
It is used to make calls, schedule meetings and organize workflow.