Outlook Copilot Chat is coming to shared and delegate mailboxes — who sees what before we roll it to EAs?

You’re right to treat “Copilot Chat on my mailbox” and “Copilot Chat on the board inbox” as different privacy conversations. Exec assistants and shared-mailbox operators already see more than most people; adding a chat surface that summarises that mailbox does not invent new access — it makes existing Full Access feel faster and more complete.

Here’s what’s going on. Roadmap 573698 (Outlook: Copilot Chat available in shared and delegate mailboxes) is In development, with general availability targeted for November 2026. The MRC description is clear enough for GRC: shared-mailbox users and delegates with read and manage (Full Access) and/or mail folder-level permission will be able to open Copilot Chat directly from those shared and delegate mailboxes in classic Outlook, when the mailbox is added as a resource. Clouds listed include Worldwide, GCC, GCC High and DoD; platform is Desktop. Treat Message Centre and the Support article Use Copilot in shared mailboxes and delegate mailboxes as the living how-to once it ships — Learn is still thinner on the classic-Outlook resource UX than the MRC blurb.

Microsoft’s Copilot requirements already say Copilot can use content a user is permitted to access in archive, shared and delegate mailboxes. Copilot Chat in Outlook gives eligible Microsoft 365 users organisational grounding over inbox, calendar and related content even without a Microsoft Copilot (Premium) licence; broader Graph/Work IQ grounding still needs the licensed Copilot experience. Shared mailboxes themselves do not get a separate Copilot “seat” — the signed-in user does. Group mailboxes remain out of scope for Copilot.

This is Schofield’s Third Law with a shared inbox attached: the easier it is for you to access your data, the easier it is for someone else to access your data — and Full Access plus Copilot Chat is convenience with a longer memory. Steady before scale puts GRC and Security in front of “turn it on for every EA.”

Options that actually work:

1. Inventory Full Access and folder delegates first. List who can open which shared and exec mailboxes today (EAs, deputies, service accounts, temporary projects). Copilot Chat will ride those permissions; shrinking or documenting the list is the control, not a mythical shared-mailbox licence toggle.
2. Pilot with named personas, not “all Outlook classic users.” Pick one EA cohort and one shared inbox with a clear owner, write what prompts are in policy (summarise overnight mail, draft replies for human send — not silent send), and check Purview audit of Copilot interactions for those users before a wider wave.
3. Separate Chat eligibility from Premium expectations. Brief leadership that 573698 is Copilot Chat in the shared/delegate context, not a free upgrade to full Microsoft Copilot licensing across Graph. Licence and data-scope questions stay with the signed-in user’s entitlements.
4. Hope nobody asks Copilot to summarise Legal@ or CEO@. Fast — until a well-meaning deputy prompts across a mailbox they had Full Access to “just in case.”

12 Panes action / comms: Tell Security: No new god-mode — Chat grounds on mail the signed-in user can already open; our risk is over-granted Full Access, not a secret Copilot service account. Tell GRC: Register shared and delegate mailboxes in the AI/agent register the same way you register high-risk sites — owner, allowed prompt patterns, retention expectations. Tell EAs: You can ask Copilot about mail you already see; you do not get mail you were never granted; keep Needs approval habits on anything that leaves the organisation. Leadership: This is Steady Adoption for assistants, not seat spray for every shared alias.

Benefits / risks: Assistants and shared-inbox teams stop swivel-chairing between folders and chat; Classic Outlook resource UX and archive behaviour may still need tenant testing (practitioner threads already debate archive grounding prompts); Support and Learn detail will lag MRC until GA; Purview DLP for Copilot locations and mailbox permissions remain the compliance backstop — verify them for your SKUs before you call privacy closed.

I’d suggest a short Steady tabletop this month: pick one shared mailbox and one delegate setup, walk Security through who has Full Access today, run three approved prompts in classic Outlook once the feature appears in your ring, and only then expand. Once people have seen what “Chat in the shared mailbox” actually summarises, the GRC habit tends to stick.

DIGITAL SKILL WORKS LTD / 12 PANES · You ask, we answer