Microsoft says a coding issue is behind a now-resolved Microsoft 365 outage over the weekend that affected Outlook and Exchange Online authentication.
According to an incident report published in the Microsoft 365 admin center on Saturday at 09:29 PM UTC, the incident also triggered Teams and Power Platform degraded functionality and caused Purview access issues and errors.
These issues were addressed by reverting the buggy code change tagged as the preliminary root cause of the widespread outage that started at 8:40 PM UTC and ended around 9:45 PM UTC.
“A recent update to Microsoft 365 authentication systems contained a code issue, resulting in impact to some Microsoft 365 apps and services,” the company said on Saturday after resolving the authentication and access problems.
“Following our reversion of the problematic code change, we’ve monitored service telemetry and worked with previously impacted customers to confirm that service is restored.”
Redmond says a preliminary post-incident report should be published later today. The company will also review the change management process to understand why the buggy change wasn’t detected during testing.
While Microsoft resolved the Microsoft 365 authentication problems over the weekend, another advisory published on the admin center states that Exchange Online users still have issues accessing their calendar entries and email messages using the iOS native mail app.
“Users may be able to click ‘continue’ when prompted and navigate back to re-entering their password to attempt to resolve impact. Additionally, some users may be able to bypass the prompt to sign-in by clicking ‘edit settings’ and then entering into the app,” the company explained.
“We’ve so far been unable to identify any Microsoft service updates which we believe are contributing towards impact. However, we’ve observed through analysis of telemetry that an accumulation of authentication token errors associated with a third-party application may be causing the issue,” Redmond added 12 hours after acknowledging the incident.
In January, Microsoft also reverted a networking configuration change behind widespread connectivity issues, timeouts, connection drops, and resource allocation failures impacting Azure services for East US 2 customers between January 8 and January 10.
More recently, on February 25, Microsoft fixed another issue caused by a DNS change that triggered Entra ID DNS authentication failures for customers using its Seamless SSO and Microsoft Entra Connect Sync.
