Microsoft is investigating an Exchange Online outage that is disrupting email delivery and preventing some customers from signing in to its cloud-based messaging service.
The incident, recorded in Microsoft’s administration centre as EX1464935, was acknowledged at 5.30pm UTC after a surge of reports from affected users. Downdetector indicated that tens of thousands of people were experiencing problems with Outlook email and access to Exchange Online.
Users have reported delays or failures when sending and receiving messages, along with authentication errors when attempting to use Exchange Online services. Some administrators are also unable to access management tools or carry out routine actions.
Microsoft said the disruption was causing intermittent failures involving mailboxes and message-delivery processes. It has not yet specified which regions are affected.
In its latest update, the company said it had identified “a common failure pattern across affected Exchange Online requests that is associated with authentication and protocol connectivity”.
Microsoft said it was examining service telemetry to establish the underlying cause, assess the full extent of the problem and test possible remedies.
The outage comes after several recent Exchange Online incidents. In June, Microsoft resolved a widespread problem affecting the mail-flow pipeline for customers in North America, Asia-Pacific and Europe.
In April, the company also addressed intermittent mailbox-access problems affecting some Outlook mobile and macOS users, as well as a separate disruption that prevented access through Outlook on the web, Outlook desktop and Exchange ActiveSync.
Microsoft has not given a timetable for a full restoration of the service.
