Outlook is facing problems on Thursday morning.
Users report that they cannot log in.
Microsoft has announced on Twitter that it is aware of the malfunction.
"We've been getting word that people are having issues with their Exchange Online accounts through Outlook on the web."
The company says users around the world have been affected.
In the Netherlands, thousands of reports were already received via Allestoringen.nl on Thursday morning.
It is not known how the failure originated.
Nor is it clear when the problems will be solved.
Two days ago, Office 365 also had a major global outage.
As a result, people could not log in to various Microsoft services for hours.
The malfunction was caused by a change that had been implemented in the underlying systems.