Microsoft is facing yet another major service outage , this time in Exchange Online , which is periodically affecting users' access to their mailboxes via the IMAP4 protocol . The incident, internally recorded as EX1215307 , was first identified on Wednesday evening and has already raised alarms for businesses and organizations that rely on legacy email clients and automated systems .
What exactly is happening with IMAP in Exchange Online?
According to Microsoft, the issue only affects IMAP4 connections, while other access methods remain unaffected. The company informed users that in several cases, repeated connection attempts may temporarily restore access to email, which indicates an intermittent rather than global failure.
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Although Microsoft has not yet provided a clear picture of the number of affected users or the geographical areas where the problem is located, the incident has been classified as an “Incident” in the Microsoft 365 admin center. This is a category usually assigned to problems with a substantial impact on productivity.
Incorrect configuration and code conflict in focus
The root of the problem, according to the official update, is found in a recent code development related to IMAP authentication support. This change contained a code conflict, which led to incorrect authentication, causing inconsistent behavior when attempting to access mailboxes.
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Microsoft says it has already begun developing a fix, which is being gradually applied to production environments. The full process is expected to be completed by the next scheduled status update, but no exact timeline for a final resolution has been given.
Why IMAP remains critical for many organizations
Despite Microsoft's clear shift towards modern access methods and APIs, IMAP is still widely used. Many businesses rely on legacy email clients, archiving systems, tracking tools, or automated workflows that haven't migrated to the modern Microsoft 365 ecosystem.
This makes such outages particularly problematic, as they affect not just email reading, but entire business processes that rely on the continuous flow of data.
Another episode in a holiday chain
The new incident adds to a series of issues Microsoft has faced in recent months. In November, Exchange Online was affected by an outage that prevented access through classic Outlook for desktops, while in late October a widespread DNS failure hit both Azure and Microsoft 365, causing an inability to connect to corporate networks and critical services.
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A few weeks earlier, in early October, issues with the Microsoft Entra authentication mechanism and multi-factor authentication (MFA) had led to an inability to access Teams, Exchange Online, and the admin center.
Cloud reliability and growing concerns
The frequency of such incidents is reigniting the debate around the resilience and complexity of cloud services . While outages are inevitable in infrastructures of this size, organizations are being urged to reconsider business continuity strategies, alternative access methods, and incident response plans.
Source: www.bleepingcomputer.com
