Microsoft Exchange Online Outage Disrupts IMAP4 Mailbox Access

An Exchange Online service failure that occasionally prohibits users from accessing their mailboxes using the Internet Mailbox Access Protocol 4 (IMAP4) is being addressed by Microsoft.

The event that took place which was recorded under EX1215307, started at 19:00 UTC on January 1st. Microsoft noted that other connection methods remain unaffected and advised individuals affected to try again in order to get their emails back.

Microsoft confirmed the remedy was fully implemented by the morning of January 8, 2026, after the problem was initially identified on Wednesday, January 7, 2026.

The impact of this incident to users when using IMAP4 clients to sync or log in to mailboxes, users encountered sporadic failures. Other communication techniques, such mobile apps that use contemporary protocols or Outlook on the Web (OWA), were unaffected.

Microsoft stated that these persistent problems, which are brought on by a code conflict that generated an authentication misconfiguration, have already been fixed.

Microsoft further stated that there was a recent IMAP deployment related to authentication support contains a code conflict that introduced a configuration issue and is causing intermittent mailbox access issues for some impacted users. “We’re continuing to deploy the configuration change and expect this process to complete by our next scheduled update.”

This ongoing IMAP4 access issue has been reported as an incident in the Microsoft 365 admin centre, a flag often applied to serious service difficulties with obvious user impact, however Microsoft has not yet disclosed which areas and how many users are affected.

In November, Microsoft addressed a similar Exchange Online outage that prevented users of the traditional Outlook desktop client from accessing their mailboxes.

The November incident came after a significant DNS outage in late October that affected Microsoft 365 and Azure services, making it impossible for customers to access various applications and platforms and log into enterprise networks.

A few weeks prior, in early October, Microsoft resolved another outage that prevented users from using Microsoft Entra single sign-on (SSO) login to access Microsoft Teams, Exchange Online, and the admin centre because of Multi-Factor login (MFA) problems.

Microsoft has cancelled plans to impose a daily cap of 2,000 external recipients on Exchange Online bulk email senders, which were announced in April 2024.

Microsoft shared an update on January 8, 10:48 EST, where it was verified and confirmed that the problem has been resolved following a configuration modification on all impacted servers that “reduced volume and restored normal service functionality.” 

For immediate action for users who still experiences this issue, Microsoft suggests a straightforward retry or utilising Outlook on the Web as a temporary workaround if you are still having connectivity problems.

Also for admin diagnostics by using the Microsoft 365 Service Health Dashboard, administrators can conduct automated connectivity tests or keep an eye on ongoing health.

Only a few months prior to Microsoft’s planned permanent termination of Basic SMTP authentication support on March 1, 2026, this outage took place. As a result, all users will need to switch to OAuth 2.0 for safe connections.