Several Microsoft 365 users reported issues accessing Outlook on Sunday, with many taking to social media to express their concerns. The outage, which affected thousands, also impacted other Microsoft 365 services. Microsoft acknowledged the issue and confirmed it was investigating the outage. The company later stated that it had rolled back a service update that had caused the disruption and confirmed that the services had been restored. 

Explaining the situation, Microsoft 365 Status posted on X, “We're investigating an issue in which users may be unable to access Outlook features and services. Additional details can be found under MO1020913 in the admin center”. 

Providing further updates, the company stated that it was reviewing data from its monitoring systems and user reports to assess the impact. Microsoft tweeted, “We’re reviewing available telemetry and customer provided logs to understand the impact. We’ve confirmed this issue is impacting various Microsoft 365 services. Refer to MO1020913 for more detailed information”.

After identifying a possible cause, the company took corrective action and confirmed the rollback of the suspected faulty update. It tweeted, "We've identified a potential cause of impact and have reverted the suspected code to alleviate impact. We’re monitoring telemetry to confirm recovery. Refer to MO1020913 for more detailed information".

After rolling back the problematic update, Microsoft confirmed that most affected services were recovering. The tweet read, “Our telemetry indicates that a majority of impacted services are recovering following our change. We’ll keep monitoring until impact has been resolved for all services. Refer to MO1020913 or https://portal.office.com/ServiceStatus for more detailed information”.

Later, Microsoft confirmed that the issue had been fixed and that normal service had resumed. The company reassured users with a final update, stating, “Following our reversion of the problematic code change, we’ve monitored service telemetry and worked with previously impacted users to confirm that service is restored. Please refer to MO1020913 in the admin center for detailed information". 

According to Downdetector, a website that tracks service disruptions, nearly 37,000 users in the U.S. reported being unable to access Outlook during the outage.