'%3e%3cpath%20d='M8%200C12.4183%200%2016%203.58172%2016%208C16%2012.4183%2012.4183%2016%208%2016C3.58172%2016%200%2012.4183%200%208C0%203.58172%203.58172%200%208%200ZM11.6162%204.38379C11.2257%203.99337%2010.5927%203.99338%2010.2021%204.38379L8%206.58594L5.79785%204.38379C5.40732%203.99334%204.77429%203.99329%204.38379%204.38379C3.99331%204.77429%203.99335%205.40733%204.38379%205.79785L6.58594%208L4.38379%2010.2021C3.99348%2010.5927%203.99341%2011.2257%204.38379%2011.6162C4.77426%2012.0066%205.40734%2012.0065%205.79785%2011.6162L8%209.41406L10.2021%2011.6162C10.5927%2012.0066%2011.2257%2012.0067%2011.6162%2011.6162C12.0067%2011.2257%2012.0066%2010.5927%2011.6162%2010.2021L9.41406%208L11.6162%205.79785C12.0066%205.40735%2012.0066%204.77429%2011.6162%204.38379Z'%20fill='%23080E17'%20fill-opacity='0.46'/%3e%3c/g%3e%3cdefs%3e%3cclipPath%20id='clip0_3761_713'%3e%3crect%20width='16'%20height='16'%20fill='white'/%3e%3c/clipPath%3e%3c/defs%3e%3c/svg%3e)
Fix On-Premises Users Cannot See Microsoft 365 Free/Busy Information
Question details
On-premises Exchange users are unable to view the free/busy calendar status for Microsoft 365 mailboxes in an Exchange hybrid environment.
- Product
- Microsoft Exchange Hybrid / Microsoft 365
- Device & OS
- not provided
- Scenario
- Users are trying to schedule meetings or view calendar availability across a hybrid Exchange deployment.
- Observed behavior
- The free/busy calendar information of Microsoft 365 users appears as unavailable, hashed out, or throws an error to on-premises users.
Ensure that you have administrator access to both your on-premises Exchange Server and your Microsoft 365 tenant, and verify that the target users have correctly configured their default calendar sharing permissions.
Verify Autodiscover and Organization Relationship Configurations
Check that Autodiscover is correctly routing requests and that the organization relationship between the on-premises environment and Exchange Online is valid.
Free/busy lookup failures in a hybrid environment are often caused by misconfigured Autodiscover endpoints or broken organization relationships.
By validating the TargetAutodiscoverEpr and testing connectivity, you can identify where the cross-premises request is failing.
Run the Microsoft Remote Connectivity Analyzer (ExRCA) from the Microsoft website. Select the 'Free/Busy' test to ensure the Autodiscover service is functioning correctly for the routing domain.
Log in to the Exchange admin center. Navigate to the 'Organization' tab and verify that the organization relationships exist between on-premises and Exchange Online, and that 'Free/busy access' is explicitly enabled.
Open the Exchange Management Shell and run 'Get-OrganizationRelationship | Format-List TargetAutodiscoverEpr'. Ensure that the URL returned points to the correct Exchange Online Autodiscover endpoint.
Consult Microsoft Q&A Exchange Hybrid Specialists
Since hybrid deployments are highly complex, deeper configuration issues involving OAuth or granular permissions should be reviewed by Microsoft Exchange specialists.
Looking for a Lightweight and Reliable Office Suite? Try WPS Office
While you troubleshoot complex Exchange Server backend configurations, you might also be looking for a reliable, cost-effective office suite for your organization's daily document tasks. WPS Office provides a lightweight, highly compatible alternative to Microsoft Office.
Frequently Asked Questions
Why does free/busy information only fail in one direction in a hybrid deployment?
This typically occurs if the Autodiscover record, OAuth configuration, or Organization Relationship is misconfigured on one side of the deployment (either on-premises or Exchange Online) but is functioning correctly on the other side. Each direction relies on its own set of validation checks.
Does OAuth configuration affect free/busy lookups in Exchange Hybrid?
Yes. Exchange Server uses OAuth authentication to securely request free/busy information across premises. If the intra-organization OAuth certificate is expired, missing, or improperly configured, free/busy requests will be denied and return an error.
How do I know if my Hybrid Configuration Wizard (HCW) caused the free/busy issue?
If free/busy lookup was working previously and stopped immediately after updating or re-running the HCW, the wizard may have overwritten custom organization relationship settings or failed to correctly publish the current OAuth certificate. Reviewing the HCW logs can help identify the failure point.
