The Microsoft office building is in the RheinauArtOffice in Cologne, Germany, on September 11, 2025.
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Microsoft on Thursday resolved technical issues that got in the way of people sending and receiving email messages in its Outlook application and completing other tasks.
The event started in the middle of U.S. business hours, leading people to address the snafu on social media as schools, government institutions and companies dealt with the outage. It lasted nearly 11 hours. Outlook represents a core part of Microsoft 365 productivity software bundles.
At 2:37 p.m. ET, the company said in an X post that it was investigating an issue affecting Outlook.
“Users may be receiving a ‘451 4.3.2 temporary server issue’ error message when attempting to send or receive email through Outlook,” Microsoft said in an update to an online dashboard.
In addition, searches in the OneDrive cloud file storage application, the Teams communication app and the SharePoint Online collaboration service might be slow or might not work at all, the company said on the dashboard. Microsoft said people might also be unable to create chats, meetings, teams, channels, breakout rooms or live events in Teams.
In an X post published at 3:17 p.m. ET, Microsoft said that it had found that “a portion of service infrastructure in North America” was not handling traffic correctly and that it was trying to fix the problem.
A follow-up post at 4:14 p.m. ET said that the company has restored affected infrastructure and was directing traffic to other infrastructure to recover.
“We’re seeing continued improvements in service availability and functionality as a result of our load-balancing efforts,” Microsoft said in an X post at 9:46 p.m. ET. “We’re actively monitoring performance and making targeted adjustments to further improve stability and availability, while continuing recovery actions to ensure a reliable service experience.”
Microsoft said at 1:29 a.m. ET that it had resolved the issues.
Last July, an Outlook outage lasted over 21 hours.
