The Microsoft office building is in the RheinauArtOffice in Cologne, Germany, on September 11, 2025.
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Microsoft said Thursday that it was working to resolve technical issues that were getting in the way of people sending and receiving email messages in its Outlook application.
The event happened 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. The program 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 and the SharePoint Online collaboration service might be slow or might not work at all, the company said on the dashboard.
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 working 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.
Last July, an Outlook outage lasted over 21 hours.
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