The remote working platform, which is part of Office 365, experienced issues across Europe on Monday, where many businesses have told employees to work from home when possible.
"We're investigating messaging-related functionality problems within Microsoft Teams," the tech giant said.
The issue appears to stem from the huge influx of new users, which typically has around 20 million daily users around the world.
The platform recently lifted restrictions on the free version, as well as extended the month-long free trial for the premium version to six months.
Other remote working apps and tools suffered similar issues, with online video conferencing service Zoom experiencing an outage earlier on Monday.
It is the second major outage to hit Microsoft Teams this year, following a three-hour shut down last month due to an unrenewed security certificate.
Microsoft's Xbox Live platform also went down briefly on Sunday, most likely as a result of an increase in demand.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies