Availability (free/busy) fails for delegated mailboxes in Exchange hybrid deployments that use Graph API only
In a classic hybrid deployment that's configured by using ConfigureExchangeHybridApplication.ps1 -UseGraphApiOnly, availability (free/busy) information fails when a remote mailbox user accesses a delegated on-premises mailbox and checks the availability of mailboxes that are hosted in Exchange Online. When this issue occurs, you experience the following symptom, depending on the UI. Classic Outlook: The following error message is displayed: “Your server location could not be determined. Contact your administrator.”; Outlook on the web (OWA): The following error message is displayed: “No information"; Exchange EWS logs: The following error is recorded: "The remote server returned an error: (403) Forbidden." EXNL-GraphWebRequestProcessingException:WebException.
Other open issues in Exchange
All known issues- Availability (free/busy) fails for delegated mailboxes in Exchange hybrid deployments using Graph API onlyOpen · Exchange Server update known issues
- showInAddressList property is out of sync with Microsoft ExchangeOpen · Microsoft Graph known issues
What changed
First observed 14 Oct 2026No field changes in the recorded history.
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