In Outlook Classic and New, the copilot button does not appear for shared or delegated accounts. It does appear on the web version.

Hi @Vicente B,

Thank you for the update and for providing the screenshots.

Given the scale of impact in your organization and the fact that the behavior differs from what is observed in my environment, I recommend opening a support case with Microsoft Support for further investigation.

For business support:   

1. Find your Microsoft 365 admin: If you don't know who the global admin is in your organization, you can find guidance here: How can I find my Microsoft 365 admin? - Microsoft Support    
2. Submit a service request: The Global Administrator should create a support request with Microsoft to receive advanced technical assistance. For detailed instructions, see: Get support - Microsoft 365 admin | Microsoft Learn    

If your subscription is from a partner or reseller, contact the reseller's support provider to help open a service request on behalf of you instead.    

When contacting support, I suggest including:

• The screenshots you shared showing Copilot available in the primary mailbox and unavailable in the shared mailbox.
• The Outlook version and build information.
• Details on how the shared mailboxes are configured (Full Access + Send As permissions).
• Confirmation that the issue affects multiple users and shared mailboxes.
• Confirmation that the same shared mailbox works correctly in New Outlook and OWA.

This information should help the support team determine whether this is a tenant-specific issue, a Classic Outlook limitation, or a bug requiring review by the Outlook engineering team.

Please feel free to share any updates from Microsoft Support, as the outcome may be helpful to other community members experiencing similar behavior.

Best regards.

Hello,

We can see that there are changes in version 2608 (build 20326.20142), but the functionality is still not working for us.

Regarding your questions:

1. When you tested the mailbox as a standalone account, was the shared mailbox configured to allow direct sign-in, and was it added to Outlook as a separate authenticated account? We added the shared mailbox as a standalone account, but authenticated using the primary mailbox credentials (Full Access + Send As permissions). The reason for this configuration is the volume of emails, as we do not want to exceed the 40 GB OST file limit.
2. 1. 1. Were you able to sign in directly using the shared mailbox credentials, or was the mailbox still being accessed through shared/delegated permissions from another user's account?
      Due to auditing requirements, we are not permitted to sign in using the shared mailbox credentials.
   2. Does the issue occur with all shared/delegated mailboxes, or only with specific ones? It occurs with all shared mailboxes.
      1. Does this behavior affect multiple users or only one user?
      It affects all users who work with shared mailboxes (more than 5,000 users).
      1. Have all affected users been assigned a Microsoft 365 Copilot license?
      Yes.
      1. Does the Copilot button disappear in both Outlook Classic and New Outlook for all affected users?
      This issue only occurs in Outlook Classic. It does not occur in New Outlook, OWA, or iOS.
   3. Additionally, could you provide some screenshots of the behavior? Primary (named) account:
      • 
   4. Shared mailbox:
   6. If possible, please use the same shared/delegated mailbox in Outlook on the web (OWA) and provide a screenshot showing that the Copilot experience is available there.
      • 

Gracias.

Hello @Vicente B,

Based on Microsoft's current documentation, Microsoft 365 Copilot Chat in Outlook is expected to support shared and delegated mailboxes, including scenarios where users have Full Access or folder-level permissions. Copilot features such as Draft and Summarize should be available when working in eligible shared or delegated mailboxes.

For your reference: Shared and Delegated Mailboxes with Microsoft 365 Copilot Chat in Outlook | Microsoft Support

I have been attempting to reproduce this behavior in my test environment; however, so far I have been unable to reproduce the issue, and the feature appears to be working as expected for shared and delegated mailboxes. Before jumping to any conclusions, I'd like to gather a few additional details to better understand your scenario.

Could you please help clarify the following:

• When you tested the mailbox as a standalone account, was the shared mailbox configured to allow direct sign-in and added to Outlook as a separate authenticated account?
• Were you able to sign in directly using the shared mailbox credentials, or was the mailbox still being accessed through shared/delegate permissions from another user's account?
• Is the issue occurring with all shared/delegated mailboxes, or only specific ones?
• Does the behavior affect multiple users or only a single user?
• Are all affected users assigned a Microsoft 365 Copilot license?
• Does the Copilot button disappear in both Classic Outlook and New Outlook for all affected users?
• Additionally, could you provide a few screenshots of the behavior?
  • The shared/delegated mailbox selected in Outlook where the Copilot button is missing.
  • The primary mailbox in the same Outlook profile where the Copilot button is available.
  • If possible, the same shared/delegated mailbox in Outlook on the web showing the Copilot experience available.

These details will help determine whether the issue is related to a specific mailbox configuration, permission model, licensing, or a potential Outlook Windows client issue.

Thank you for your information and I look forward to your next update.

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