Network and IT administrators faced ongoing Microsoft 365 issues this week, reporting that some end users are unable to use Microsoft Outlook or other Microsoft 365 applications.

The problems started on Monday, with many administrators contacting BleepingComputer to say that some of their users were experiencing disruptive issues in Microsoft Outlook, the program not opening, crashing after opening, seeing delays in mail delivery or errors indicating that there is no valid license associated. with the user.

These same issues have been confirmed by other admins on Reddit [1, 2, 3] and in the Microsoft Forums.

“Anyone having problems with the office? We have a department using HP probook 450 G9, everyone is experiencing Outlook, Word, etc. being very slow and unresponsive,” reads one post on Reddit.

“The status page doesn’t list these symptoms, but many users in my organization are reporting that they can’t sign in to Teams or Outlook. Switching their licenses from Business Basic to e1 seems to let them in. Someone did one hear anything?” another post on Reddit reads.

“Have a few users who can’t sign in and authenticate with desktop apps. Some connections to Microsoft seem completely broken to them…even defender scans when installing new software reports that it doesn’t ‘is unable to log in. Weather widget is down. OneDrive, Teams, Word… all down. But they can use browser versions,’ commented another administrator.

Most complaints received by BleepingComputer relate to Microsoft Outlook, but there are also reports of users experiencing crashes and freezes in Word, Excel, and Teams.

Although Microsoft has not publicly shared any information about these issues and has yet to respond to a request for additional information from BleepingComputer, some administrators have offered various solutions that have helped resolve issues on their network.

Workarounds shared by various admins in the above Reddit threads include:

• Make sure Outlook, SharePoint, or other Microsoft 365 apps are enabled for users in the Azure AD tenant.
• Remove and re-add Microsoft 365 licenses to affected users.
• Disable the Internet Protocol Version 6 (TCP/IPv6) setting in the workstation network adapter properties.
• Uninstalling EDR security software seems to improve performance (not recommended).

However, these workarounds did not work for everyone.

“No Mac reports here, but Windows reports keep coming. Tried removing/re-adding users’ A3 licenses in Azure AD based on other comments, but to no effect,” share an administrator today.

For this reason, some administrators have switched affected users to Outlook on the web (OWA) until these issues are resolved.

What’s so frustrating about this issue is that it doesn’t affect all tenants or even all users in a tenant, making it difficult to track down the exact cause of the problem.

On Tuesday, Microsoft provided a workaround for a problem with Microsoft Outlook which also causes performance issues and freezes when launching the application.

“A known cause for this symptom is cache reseeding. This is expected if the user has created a new profile or manually switched from REST to MAPI by disabling shared calendar enhancements,” Microsoft said.

“However, due to endemic issues reading service-enabled feature state in non-Office MAPI-based applications, running such applications may force this switch unexpectedly.”

However, it’s unclear whether this is the same issue reported by admins or a different one, as there’s no mention of missing licenses or issues with other Microsoft 365 apps.

BleepingComputer contacted Microsoft again to see if they are aware of the issue and if there are any workarounds, but no response was immediately available.