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Is Microsoft 365 IMAP down right now for everyone?
Microsoft 365 Advisory: Resolving IMAP4 Mailbox Access Failures (January 2026)
Administrators and users relying on the IMAP4 protocol within Microsoft 365 environments should be aware of a recent service degradation that occurred in early January. While Microsoft has signaled a resolution, understanding the root cause is critical for IT teams troubleshooting lingering connectivity issues.
Incident Overview
On the afternoon of January 8, 2026 (CET), Microsoft 365 services experienced a specific disruption affecting mailbox accessibility. This issue was isolated strictly to connections made via the Internet Message Access Protocol (IMAP4). Users attempting to sync email through legacy clients or applications dependent on IMAP4 encountered intermittent failures or complete inability to connect.
Other connection methods, such as MAPI (Outlook Desktop), Exchange ActiveSync (mobile), and Outlook on the Web (OWA), remained fully functional.
Technical Root Cause
According to the official status message EX1215307 released in the Microsoft 365 Admin Center, the disruption stemmed from a vendor-side deployment.
- Trigger: Microsoft rolled out a recent update targeting IMAP authentication support.
- Conflict: This deployment introduced a code conflict within the authentication architecture, resulting in a misconfiguration on specific servers handling IMAP traffic.
- Symptom: The configuration error prevented successful handshakes between the client application and the Exchange Online server, causing the “temporarily unable to access” errors.
Resolution Status
As of January 9, 2026, at 7:56 AM, Microsoft confirmed the deployment of a configuration fix across the affected infrastructure. Telemetry indicates that error rates have subsided and normal service functionality is restored.
Actionable Advice for Administrators
- Verify Resolution: Although the incident is marked as resolved, test critical IMAP-dependent applications (e.g., ticketing systems, legacy CRMs) to ensure connection stability.
- Retry Strategy: If users still report errors, advise them that the issue was transient. A simple restart of the email client or a forced re-sync often clears cached connection failures.
- Modern Authentication Check: Since the root cause involved authentication support, ensure your tenant is not relying on deprecated Basic Authentication methods, which are often the target of such infrastructure updates.