Microsoft 365 Outage Resolved After 30 Hours—Root Cause: 'Network Configuration Change'

The Microsoft (MS) cloud outage that halted offices worldwide has been officially resolved. On the 14th at 2 p.m. (Korea time), MS concluded the incident as "service recovery complete." According to MS records, the outage was resolved at 1:10 a.m. on the 14th. Depending on the starting point, it was a major outage lasting approximately 30 hours at most from the evening of the 12th, or conservatively around 24 hours. Domestically, reports of the outage surged from 2:39 a.m. on the 13th, but MS's final record traces the start of the outage back to the evening of the 12th.

Root Cause: "Past Problem Surfaced After Configuration Change"

Through preliminary investigation results, MS clarified that the outage was "a technical issue unrelated to cyberattacks or artificial intelligence (AI)." It explained that a problem that arose during past network capacity expansion was brought to the surface following a recent network configuration change. Following the Amazon Web Services (AWS) and Azure outages last month, this incident again had 'configuration change' as the trigger. MS announced it would release a preliminary post-incident report within two business days and a final report within five business days.

Delayed Emails Continue Even After Recovery Declaration

The recovery declaration does not immediately mean a complete return to normalcy. Reports on the 14th indicated that access delays and email delivery issues persisted in some regions and for some customers. Because MS extended the email transmission waiting time to 48 hours during the outage, residual effects remain as emails caught during the outage are being delivered sequentially through the weekend. Even if an email sent yesterday arrives today, it is safer to avoid resending rather than risk duplicate delivery.

7.4 Million Reports Across 90 Countries, Largest in One Year

The scope of impact was broad. According to network analysis firm Ucloudア, reports of this outage exceeded 7.4 million cumulatively across approximately 90 countries, marking the largest scale in the past year. The U.S. House of Representatives' computer network and the UK's National Health Service (NHS) were affected, New Zealand halted visa issuance, and Taiwan's financial firms operated via fax. U.S. public company Workhorse postponed earnings announcements. This was the cost the world incurred in one day from entrusting email, meetings, and documents to a single company.

"Deeply Apologizes"…Compensation Is Not Automatic

Through its official account, MS stated it "deeply apologizes and takes responsibility seriously," and promised Service Level Agreement (SLA) credit compensation. Typically, credits equivalent to 25-100% of monthly fees are disbursed in proportion to affected services and duration. However, compensation is not automatic; customers must claim it directly. South Korean companies that experienced business disruptions from this outage should organize damage records during the outage timeframe and proceed with the claim process. Despite the apology, online mockery of "MS364"—suggesting one day was missing from 365 days—has spread.

The questions this outlet raised the previous day remain. Do you have a backup plan when the cloud goes down? This time it was 30 hours. Next time it could be longer.