Microsoft is investigating service issues preventing users from accessing their Microsoft 365 accounts and blocking access to installed apps.

The company confirmed the issue in a tweet shared via the Microsoft 365 Status account and pointed admins to the Microsoft 365 Admin Center for more details.

"We're investigating an issue affecting access to https://msft.it/6016gbJ06 and Microsoft 365 apps," the company said.

"Additional updates can be found at https://msft.it/6017gbJ0B under MO559201."

Affected customers report experiencing issues accessing their Outlook mailboxes and an inability to connect to the Microsoft 365 servers.

"We received reports that this impact manifested for users primarily in the North America, Poland, and United Kingdom regions, though users in other regions also may have been affected," the company said in the MO559201 alert.

Last month, another Microsoft 365 outage caused Exchange Online connectivity issues for users in North America.

In March, one more service outage blocked Exchange Online customers worldwide from sending and receiving emails or accessing their mailboxes.

A massive outage also hit Microsoft 365 in January, an incident caused by router packet forwarding issues within Microsoft's Wide Area Network (WAN) after a faulty router IP address update.

Update: Microsoft says the issues have been addressed.