Update October 16, 2026: For more information related to installation of October 2026 updates for Windows Server and the possible impact on Exchange Server, please see Exchange servers may become uns...
Updated Oct 16, 2026
Version 7.0
Blog Post
Additional findings regarding our previously reported Exchange Server SE incident:
We have confirmed Event ID 1006 (MSExchange Mailbox Replication, Warning), with MapiExceptionMdbOffline (ec=1142), affecting all four mailbox databases.
The first documented MAPI failure occurred on October 14 at 19:06 CEST. Event ID 1006 warnings started on October 15 at 02:44 CEST, with approximately 2,585 warnings recorded.
Managed Availability detected the database failures, but its recovery responders reported "Taking no failover action for exception type MapiExceptionMdbOffline" and "Taking no bugcheck action".
No Monitoring Overrides were found, and the KillServer responder was enabled before the incident.
A manual reboot restored service. KB5126655 remains installed on Windows Server 2022.
We hope these additional findings are useful to the Exchange team investigating this issue.