Some users may have been unable to access their mailboxes using Internet Mailbox Access Protocol 4 (IMAP4)
ID: EX1215307
Issue type: Incident
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Impacted services
Exchange Online
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Details
Title: Some users may have been unable to access their mailboxes using Internet Mailbox Access Protocol 4 (IMAP4)
User impact: Users may have intermittently been unable to access their mailboxes using IMAP4.
More info: Impact was specific to IMAP4, other connection methods were not impacted. Additionally, if users were actively facing this issue, retries may have been successful.
Final status: We’ve completed deploying the configuration change on the affected servers, which reduced volume and restored normal service functionality. After a period of monitoring, we’ve confirmed that impact has been fully remediated.
Scope of impact: Some users that were attempting to access their mailboxes using IMAP4 may have been intermittently impacted.
Start time: Friday, January 2, 2026, at 12:00 AM UTC
End time: Thursday, January 8, 2026, at 11:30 AM UTC
Root cause: A recent IMAP deployment related to authentication support contained a code conflict that introduced a configuration issue and was causing intermittent mailbox access issues for some impacted users.
Next steps:
- We're reviewing our deployment and provisioning procedures to help prevent similar problems in the future.
This is the final update for the event.
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