Outlook Went Down This Morning, and Microsoft Still Hasn’t Brought It Back.

Thursday morning, people sat down at their desks, clicked into Outlook, and got nothing. The web app wouldn’t load the mailbox. The desktop app couldn’t connect. Phones that use the same Microsoft mail system failed too. It was the middle of the workday, and a lot of offices run on that inbox.

Microsoft confirmed the problem on its status account just before 11 a.m. “We’re investigating reports of users experiencing issues accessing Exchange Online mailboxes through multiple connection methods in the Americas,” Microsoft 365 Status wrote, pointing administrators to incident EX1550543.

That first public note made it sound like an Americas mail problem. Thirteen minutes later the company widened it. “While we’re working to mitigate impact, we’ve confirmed the issue may affect Microsoft 365 service connectivity for users in any region,” the same account wrote.

Microsoft’s own service log, as recorded in the University of Pennsylvania’s extract of official Microsoft 365 incident reports, shows the company had already opened the Exchange ticket at 9:17 a.m. The first update, three minutes later, was cautious: a “potential issue,” with another update promised within an hour. By 9:55 a.m. Microsoft had named the ways in that were failing: Outlook on the web, the Messaging API that desktop Outlook uses, Exchange ActiveSync on phones, and the REST API that a lot of other mail apps rely on.

Downdetector, which tracks user-submitted outage reports, began flagging problems with Microsoft Outlook at 10:27 a.m. Within the next hour its account also reported problems for Microsoft 365, Microsoft Copilot, the Microsoft Store, OneDrive and Microsoft accounts. Those are user reports, not Microsoft’s official list. The official list came later, and it was long enough on its own.

Four doors into the inbox, and all of them failing

This is not a spam-folder story, and it is not about mail arriving late. Microsoft said users “may be unable to connect to their mailboxes.” If the connection itself is failing, you don’t just miss a message. You can’t open the box.

At 10:45 a.m. the company said it had “identified connectivity errors occurring on a portion of Exchange Online infrastructure which receives and processes users’ access requests.” It collected networking logs and said it was still investigating the source. It has not named a root cause.

IT desks were already hearing from users. The University of Colorado Boulder’s Office of Information Technology, posting at 11:20 a.m., said it was receiving reports of a widespread issue and that faculty, staff and students “may experience intermittent connectivity issues, errors, slow performance, or an inability to access Microsoft 365 applications, including Outlook, Teams, SharePoint, and OneDrive.” It said no workaround was available and told people to retry periodically.

Microsoft’s official list did not include OneDrive. It later did include more than email.

The trouble didn’t stay in mail

At 11:19 a.m. Microsoft’s Exchange update changed tone. The affected infrastructure, it said, “is experiencing elevated load across multiple regions, which is contributing to the connectivity errors users are receiving.” The company said it was restarting and repairing the strained parts of that infrastructure “to mitigate impact,” and that it was “evaluating options to redirect traffic to alternate infrastructure to expedite relief.”

Seven minutes later it opened a second ticket, MO1550821, under the Microsoft 365 suite. That advisory said users “may be unable to connect to multiple Microsoft 365 services,” and it listed five: Exchange Online, Microsoft Teams, SharePoint Online, Microsoft Copilot 365 and Microsoft Defender XDR. In that update Microsoft also said it was “reviewing an unexpected increase in a specific type of service traffic to determine whether it’s contributing to the elevated load.” It did not say what that traffic was.

At 11:29 a.m. came the first sign of a fix being applied, not just studied. “We’ve redirected a portion of traffic away from the affected infrastructure in the US to reduce load, and we’re evaluating doing the same in other regions,” Microsoft wrote in the Exchange ticket. It added that “Exchange is the primarily impacted service,” and that the other Microsoft 365 problems were being tracked under the second ticket.

The status account posted the load finding at 11:35 a.m. and pointed the public to both incident numbers and to Microsoft’s cloud status page.

That is as far as the company had gone when this report was published. It had not said the service was restored. It had not said when it would be. The next Exchange update was due by 12:30 p.m., and the broader Microsoft 365 advisory by 1:30 p.m.

This was already Microsoft’s second mess of the morning

A separate Microsoft Teams problem had already come and gone before the mail outage became public. Microsoft opened that incident, TM1550488, after users in the Americas had trouble sending and loading chats. It later said the Teams issue started at 7:45 a.m. and ended at 8:53 a.m., and at 10:08 a.m. it told customers the impact was “fully resolved.” The preliminary explanation was “resource contention within the underlying service infrastructure.” Presence status, Microsoft said after a closer look, was not affected.

That Teams incident is a different ticket, with its own start and end. Microsoft has not tied it to the Exchange failure that followed. The earlier one is useful only as context: the same company had already spent the morning pulling a major work tool back online, and by the time it called that first problem fixed, the mailbox outage was already being investigated.

For offices trying to get through Thursday, the distinction matters less than the inbox in front of them. Mail is still the thing most of them can’t do without. Microsoft has started moving U.S. traffic off the strained equipment. Until it says the errors have stopped, a lot of people are sitting in front of a login screen that won’t let them in.