💡 Our Technical Review in summary
1. Summary
Exchange Online users utilizing the POP3 connection method may have experienced issues where email messages were not successfully deleted from the server. A package version conflict in a recent update introduced a regression that caused the POP3 QUIT command to fail specifically after a DELE (delete) operation was performed. This failure prevented the session from closing cleanly, which is required in the POP3 protocol to finalize the removal of messages marked for deletion.
2. Impact
Impact was limited to users connecting via POP3. While these users could still read and download messages, any emails they attempted to delete remained in their mailbox. Users accessing Exchange Online through other protocols (such as Outlook Desktop via MAPI, Outlook on the web, or mobile devices via Exchange ActiveSync) were not affected.
3. Status
Service Restored. Microsoft has successfully completed the deployment of a fix to all affected environments. The issue was fully resolved as of Saturday, January 24, 2026, at 5:19 AM UTC. To prevent future occurrences, Microsoft is reviewing its package provisioning and deployment procedures.
Microsoft Official Issue Details
User Impact
Users may have been unable to delete email messages after running the QUIT command through the POP3 connection method.
Status: serviceRestored
Service: Exchange Online
Classification: advisory
Origin: microsoft
Updates
- 2026-01-26 08:47
Title: Users may have been unable to delete email messages after running the QUIT command through the POP3 connection methodUser impact: Users may have been unable to delete email messages after running the QUIT command through the POP3 connection method.
More info: Specifically, POP3 users could read and download their email messages, but any messages they deleted may not have actually been removed, because the session failed to close properly. If a message was deleted on Exchange Online using the DELE command, the POP3 QUIT command may have failed, preventing the session from closing cleanly and caused messages marked for deletion to remain in the mailbox.
If the user was not using POP3, they were not impacted.
Final status: We’ve confirmed that the fix deployment has completed successfully and that the issue has been fully resolved.
Scope of impact: Impact was specific to some users attempting to delete email messages after running the QUIT command using POP3 connection method.
Start time: Tuesday, January 20, 2026, at 5:01 AM UTC
End time: Saturday, January 24, 2026, at 5:19 AM UTC
Root cause: A package version conflict introduced a regression that caused the POP3 QUIT command to fail after a DELE operation.
Next steps:
– We’re reviewing our package provisioning procedures to help prevent similar problems in the future.This is the final update for the event.
- 2026-01-23 09:13
Title: Users may be unable to delete email messages after running the QUIT command when POP3 connection method is usedUser impact: Users may be unable to delete email messages after running the QUIT command when POP3 connection method is used.
More info: Specifically, POP3 users can read and download their email messages, but any messages they delete may not actually be removed, because the session fails to close properly. If a message is deleted on Exchange Online using the DELE command, the POP3 QUIT command may fail, preventing the session from closing cleanly and causing messages marked for deletion to remain in the mailbox.
If the user is not using POP3, they are not impacted.
Current status: We’ve begun rolling out the fix and can confirm it has been successfully deployed to approximately 56% of the affected environments. We’ll continue monitoring progress and will provide an updated completion timeline as soon as it’s available.
Scope of impact: Impact is specific to some users attempting to delete email messages after running the QUIT command using POP3 connection method.
Root cause: A package version conflict introduced a regression that causes the POP3 QUIT command to fail after a DELE operation.
Next update by: Monday, January 26, 2026, at 11:00 AM UTC
- 2026-01-22 11:59
Title: Users may be unable to delete email messages after running the QUIT command when POP3 connection method is usedUser impact: Users may be unable to delete email messages after running the QUIT command when POP3 connection method is used.
More info: Specifically, POP3 users can read and download their email messages, but any messages they delete may not actually be removed, because the session fails to close properly. If a message is deleted on Exchange Online using the DELE command, the POP3 QUIT command may fail, preventing the session from closing cleanly and causing messages marked for deletion to remain in the mailbox.
If the user is not using POP3, they are not impacted.
Current status: We’ve identified an issue where a recent update introduced a conflict that prevents the POP3 QUIT command from completing after a message is deleted. We’ve validated a fix in our test environment and initiated a deployment to affected users. The deployment is progressing through a gradual rollout and we expect full completion within the next 24 to 48 hours.
Scope of impact: Impact is specific to some users attempting to delete email messages after running the QUIT command using POP3 connection method.
Root cause: A package version conflict introduced a regression that causes the POP3 QUIT command to fail after a DELE operation.
Next update by: Friday, January 23, 2026, at 10:00 AM UTC
