You are a delegate for another user in Outlook and have full calendar permissions. When you ask Copilot to schedule a meeting on behalf of that user, Copilot either refuses, generates an error, or creates the meeting on your own calendar instead. This happens because Copilot does not use the same delegation permissions that the Outlook desktop or web client uses. Instead, Copilot relies on Microsoft Graph API permissions and the user context passed during the request. This article explains why Copilot fails to schedule on behalf of another user and provides the exact steps to resolve the issue.
Key Takeaways: Fix Copilot Scheduling on Behalf of Another User
- Microsoft 365 admin center > Settings > Org settings > Copilot > Data sources: Controls which Microsoft Graph data Copilot can read for grounded responses.
- Exchange admin center > Recipients > Mailboxes > mailbox delegation > Send on Behalf: Grants the delegate permission to send messages and meeting requests on behalf of the mailbox owner.
- Outlook web > Calendar > Share > Delegate access > Editor permission: Grants the delegate calendar editor access, which Copilot requires to create and modify meetings.
Why Copilot Cannot Schedule on Behalf of Another User
Copilot in Outlook uses the Microsoft Graph API to read and write calendar data. When you ask Copilot to schedule a meeting on behalf of another user, Copilot sends an API request that includes the delegate’s identity and the mailbox owner’s identity. The Graph API checks two things: whether the delegate has the correct application-level permission and whether the mailbox owner has granted the delegate the required mailbox-level delegation rights.
Most organizations grant delegates permissions through Outlook’s sharing or delegation UI. These settings are stored in the mailbox owner’s mailbox as delegate settings. However, Copilot and Graph API require a specific combination of permissions that the Outlook UI does not always configure automatically. Specifically, the delegate must have Editor permission on the mailbox owner’s calendar, and the mailbox owner must have Send on Behalf permission granted to the delegate. If either of these is missing, Copilot will respond with an error message such as “I cannot schedule on behalf of this user” or “You do not have permission to perform this action.”
Additionally, Copilot’s data access is governed by the Copilot data source settings in the Microsoft 365 admin center. If the Copilot service is restricted to certain Microsoft Graph data sources, the API request may be blocked even if the delegate permissions are correct.
Steps to Fix Copilot Scheduling on Behalf of Another User
Follow these steps in order. Each step addresses a specific layer of permissions that Copilot requires.
Step 1: Verify and Grant Send on Behalf Permission in Exchange Admin Center
- Open the Exchange admin center
Go to https://admin.exchange.microsoft.com and sign in with an account that has Exchange admin or Global admin permissions. - Navigate to the mailbox owner’s settings
Select Recipients > Mailboxes. Find and click the mailbox owner’s display name. In the flyout pane that opens, select Mailbox delegation. - Grant Send on Behalf permission
Under Send on Behalf, click Edit. Add the delegate user. Click Save. This permission allows the delegate to send meeting requests that appear to come from the mailbox owner.
Step 2: Set Calendar Editor Permission via Outlook on the Web
- Sign in as the mailbox owner
Open Outlook on the web (outlook.office.com) and sign in with the mailbox owner’s credentials. - Open Calendar and share with the delegate
Select the Calendar icon. On the toolbar, select Share > Share calendar. In the Share with specific people field, enter the delegate’s email address. - Set permission level to Editor
In the permission dropdown, select Editor. Editor permission allows the delegate to create, read, modify, and delete calendar items. Click Share. The delegate will receive an email invitation; they must accept it.
Step 3: Verify Copilot Data Source Settings in Microsoft 365 Admin Center
- Open the Microsoft 365 admin center
Go to https://admin.microsoft.com and sign in with a Global admin account. - Navigate to Copilot settings
Select Settings > Org settings. Scroll down and select Copilot (or Copilot for Microsoft 365 depending on your tenant). - Check data source permissions
Under Data sources, ensure that Microsoft Graph is enabled. If it is disabled, Copilot cannot read or write calendar data on behalf of any user. Enable it and click Save.
Step 4: Test with a Simple Command
- Open Outlook with the delegate account
Launch Outlook desktop or web and sign in as the delegate user. - Open the Copilot pane
In Outlook, select the Copilot icon on the ribbon or in the top-right corner of the reading pane. - Send a test command
Type: Schedule a 30-minute meeting with John Doe for tomorrow at 10 AM on behalf of [mailbox owner’s name]. Copilot should create the meeting on the mailbox owner’s calendar and send the invitation on their behalf.
If Copilot Still Has Issues After the Main Fix
Copilot Creates the Meeting on Your Calendar Instead of the Owner’s
This indicates that the delegate permissions are set, but Copilot is not using the “Send on Behalf” context. The most common cause is that the delegate accepted the share invitation but the mailbox owner did not grant Send on Behalf permission in Exchange admin center. Revisit Step 1 and ensure the delegate is listed under Send on Behalf. If the delegate is listed, remove them and add them again, then wait 15 minutes for the change to replicate across Microsoft 365.
Copilot Returns “I Cannot Perform This Action” Error
This error occurs when the Copilot data source is restricted. In the Microsoft 365 admin center, go to Settings > Org settings > Copilot > Data sources and verify that Microsoft Graph is set to All Microsoft Graph data or at minimum includes Calendar. If your organization uses a custom data source policy, ensure the delegate user is included in the policy scope.
Copilot Does Not Recognize the Mailbox Owner’s Name
Copilot uses the Microsoft Graph People API to resolve names. If the mailbox owner’s profile is incomplete or if the delegate’s Outlook client has a stale address book, Copilot may not recognize the name. Ask the delegate to update their Outlook address book by selecting Send/Receive > Download Address Book in Outlook desktop, or by signing out and back into Outlook on the web.
| Item | Outlook Delegate Permissions (UI) | Copilot / Graph API Permissions |
|---|---|---|
| Permission type | Editor, Reviewer, or custom sharing permissions | Send on Behalf + Editor calendar permission |
| Configuration location | Outlook web > Calendar > Share | Exchange admin center + Outlook web |
| Required for Copilot | No | Yes |
| Applies to | Outlook desktop and web client | Copilot, Graph API, and third-party apps |
| Replication time | Instant within same mailbox database | Up to 15 minutes across Microsoft 365 |
Now you can use Copilot to schedule meetings on behalf of another user in Outlook. After you complete the three configuration steps in order, test the setup with a simple meeting request. If the issue persists, verify that the delegate has accepted the calendar share invitation and that the mailbox owner has granted Send on Behalf permission in Exchange admin center. For advanced scenarios, you can use the Microsoft Graph Explorer to test the API call directly and confirm the delegate permissions are working at the API level.