​Microsoft is investigating an ongoing outage preventing Outlook on the web users from accessing their Exchange Online mailboxes.

According to thousands of user reports on DownDetector, the issue started impacting Microsoft’s services more than two hours ago and is affecting customers attempting to log into their accounts, accessing the website, and triggering server connection problems.

“We’re investigating a potential issue with Exchange Online and checking for impact to your organization,” the company said, adding that the incident impacts “any user attempting to access Outlook on the web.”

“We’ve identified a portion of code which is throwing an error. We’re working to revert the recent code change and reviewing data from the reproduction to determine any additional next steps.”

While the company has yet to share more information on the regions impacted by this incident, it has been tagged as a critical service issue tracked under EX1036356 on the Microsoft 365 Admin Center.

Microsoft says affected users may see “Something went wrong” error messages when trying to Outlook on the web.

Microsoft is also investigating a separate incident (EX1035922) caused by a code error in a recent update that prevents some Exchange Online users from searching using Outlook on the web or the new Outlook client.

“Affected users may see the following error message ‘We didn’t find anything, try a different keyword’ when performing searches in Exchange Online,” Microsoft explains. “As a workaround, users may be able to yield results using a filter in their search criteria i.e. ‘Inbox’ under folder names, in addition to a string query.” 

​The company has also partially mitigated a week-long Exchange Online outage, which is still causing delays and failures when sending or receiving email messages. Initially tracked under EX1027675, this ongoing issue is now tagged as an incident with nearly identical impact under EX1030895.

Microsoft says it’s “limited to a small subset of messages” that will trigger NDR failures and intermittent plain text calendar invite emails with winmail.dat attachments.

Two weeks ago, Redmond linked a weekend Microsoft 365 outage impacting Outlook and Exchange Online authentication to a “code issue.” Days later, it mitigated another Microsoft 365 outage affecting Teams customers and causing call failures.

Update March 19, 15:37 EDT: Microsoft says it’s seeing improvements to service health after reverting the buggy update.

“We’re reverting the problematic code change and our service health telemetry is showing improvements to service health. We will continue monitor telemetry to track the progress of recovery and pursue any additional workstreams to expedite recovery,” it said.

Update March 19, 15:37 EDT: Microsoft says it reverted the change, and the impact has been resolved for all affected users.

“A recent configuration change intended to improve the use of browser content policies within Outlook on the web, introduced a code regression resulting in impact,” the company explained in a Microsoft 365 admin center update.

“We’ve successfully reverted the problematic code change and verified the issue has been remediated through customer confirmation and service health telemetry.”