Some Exchange Online users may intermittently be unable to view free/busy information of Exchange on-premises users

Title: Some Exchange Online users may intermittently be unable to view free/busy information of Exchange on-premises users

User impact: Exchange Online users may have intermittently been unable to view free/busy information of Exchange on-premises users.

Final status: We’ve received confirmations from affected users that the issue has been resolved after we reverted the offending configuration change.

Scope of impact: This event may have intermittently impacted some users who were attempting to retrieve external users’ free/busy information in Exchange Online.

Start time: Saturday, March 30, 2024, at 12:00 AM UTC

End time: Saturday, April 13, 2024, at 6:45 AM UTC

Root cause: A configuration change was causing incorrect results to been returned by a portion of service infrastructure that manages requests sent between Exchange Online and on-premises Exchange Online users.

Next steps:
– To help prevent similar issues, we’re taking steps to ensure that configuration changes go through more extensive testing and validation to help identify problems prior to deployment.

This is the final update for the event.