Copilot in Outlook With Shared Mailboxes: Permission Inheritance Explained

Official documentation checked October 14, 2026.

Copilot access to a shared mailbox depends on the Copilot experience and the user’s existing mailbox or folder permissions. Outlook auto-mapping is a convenience for opening a mailbox in a profile; it is not a separate Copilot authorization registration. Do not remove existing permissions or convert mailbox types merely because an AI feature is missing.

How Copilot Accesses Shared Mailbox Data

Microsoft’s dedicated Copilot Chat in Outlook guide describes shared and delegated mailbox support based on existing mailbox and folder permissions. It supports permitted folder-level access as well as Full Access and does not require an additional mailbox-specific configuration. Conversation history remains associated with the user’s primary account.

The separate Copilot app guide, dated February 2026, requires a Copilot license and says full delegate access is needed for a delegate mailbox; folder-only delegation is insufficient for that app workflow. Its prompts identify the target mailbox. Do not apply one experience’s requirements to another.

The broader Outlook Copilot FAQ still lists primary-mailbox limits for its documented scenarios. These official pages are not fully harmonized. Verify the current feature and client with your administrator rather than promising that every Outlook Copilot button supports shared mailboxes or that none do.

Exchange’s delegation documentation distinguishes Full Access from Send As and Send on Behalf. The latter two permit sending but do not grant read access. Auto-mapping uses Autodiscover to open a mailbox in Outlook; it works for individual Full Access grants, while group-based access does not auto-map. That is different from whether the group grants mailbox access.

Steps to Verify and Grant Correct Permissions

1. Identify the Copilot experience

1. Record the Outlook client, feature, account, mailbox, license, and exact error. Distinguish Chat in Outlook, the separate Copilot app, and a thread’s inline summary or drafting control.
2. Confirm that ordinary Outlook access works for the intended mailbox and folders. A missing auto-mapped entry is not proof that the user lacks all access.
3. Compare the documented requirements for that experience. If you have only folder delegation, do not request Full Access merely to match the separate app workflow when a supported folder-scoped workflow meets the need.

2. Inspect effective delegation before changing it

Have the authorized Exchange administrator review the mailbox’s delegation, relevant groups and membership, deny entries, and folder permissions. The standard read-only inspection below can show mailbox-level permissions; it does not report every folder grant or resolve every group member’s effective access:

Get-MailboxPermission -Identity "shared@contoso.com" | Format-Table User,Deny,IsInherited,AccessRights -Auto

Use the documented Exchange Online connection and permissions, substituting the approved mailbox identity. This command was not executed for this article. Follow the delegation reference for the review and grant only access that the business owner approves. Do not treat an alleged AutoMapping column or a nonexistent Get-MailboxAutoMapping command as the access test.

3. Test a permitted read-only request

In a supported Chat-in-Outlook shared-mailbox context, use an existing non-sensitive message that the account may read. In the separate Copilot app, use the documented mailbox-targeting prompt format and confirm its license/delegate requirements. Compare the response with the accessible source. Keep message sending, deletion, rules, and other actions outside the read-only test.

The Chat-in-Outlook guide currently lists direct triage actions, sending on the user’s behalf, and scheduling or updating meetings as unavailable for shared/delegated mailboxes. A draft or summary does not prove those actions are supported. Verify current rollout and the precise action before relying on it.

If Copilot Still Cannot Read the Shared Mailbox

If normal access fails too, investigate the approved mailbox/folder delegation through Exchange. If normal access works but Copilot does not, preserve the configuration and escalate with the client, feature, entitlement, mailbox context, and sanitized error. Check the current documentation and service conditions; do not assume a fixed 24-hour Graph cache or attempt to force it by removing and adding permissions.

There is no verified universal Microsoft Graph mailbox-data switch under Copilot Data sources in the sources reviewed here. Do not replace group-based delegation with individual Full Access grants, add Send As as a reading workaround, or run a mailbox-type conversion as an AI repair. Those changes can broaden privileges or disrupt an existing arrangement without resolving a feature limitation.

Copilot in Outlook with Shared Mailboxes vs Personal Mailboxes: Key Differences

This review compares current official documents and records their feature-specific differences; it has not tested shared mailboxes in a tenant. Keep permissions unchanged while resolving an unclear support boundary with Microsoft or your administrator.