Copilot in Outlook: Drafting With Send-on-Behalf Permissions

Official documentation checked October 14, 2026.

Copilot can help draft a message while you work with a shared or delegated mailbox, where that experience is supported. Permission to draft or read mailbox content and permission to send on behalf of the owner are separate. There is no documented Copilot account selector that turns a draft into another person’s identity or guarantees their signature.

Set up the mailbox access required for your work, confirm the exact Copilot experience available, then review the sender and message in Outlook before sending.

Overview of Copilot Send-On-Behalf-Of Permissions

Send on behalf is an Exchange permission. It allows a delegate to send with the delegate identified on behalf of the mailbox owner. Full Access permits mailbox management but does not itself permit sending. Send As is a separate permission that presents the mailbox as the sender. Microsoft’s recipient-permission reference defines these distinctions.

Microsoft’s current Copilot Chat in Outlook mailbox guide documents drafting and summarization while working in shared or delegated mailboxes, using existing mailbox and folder access. It lists direct sending in that experience as not yet supported. A draft suggestion does not send a message or grant Exchange permissions.

Feature coverage differs across experiences. The separate Copilot app guide describes licensed shared/delegated mailbox capabilities and a full-delegate-access requirement for that app. Do not apply that requirement automatically to every Outlook folder-sharing scenario.

Steps to Grant Send-On-Behalf-Of Permission in Exchange Admin Center

An administrator with the appropriate Exchange permissions should confirm the mailbox type and existing delegates first. A Global Administrator account is not an automatic prerequisite. Avoid replacing existing delegation when adding one authorized person.

1. Open the Exchange admin center and go to Recipients > Mailboxes.
2. Select the owner’s mailbox, not the delegate’s own mailbox. Review Mailbox delegation.
3. For a supported user mailbox, edit Send on behalf, add the approved delegate, and save. Grant only the access the delegate’s duties require.
4. For a shared mailbox, do not expect the same Send on behalf control in the EAC. Microsoft documents managing that permission through Exchange Online PowerShell. The administrator should follow the linked permission reference and preserve existing delegates; replacing its delegate list can remove other people’s access.
5. Confirm the saved permission, allow for propagation, and test normal Outlook sending to an approved test recipient. A successful Copilot draft is not the permission test.

Mailbox reading may require separate delegated folder access or Full Access, depending on the workflow. Do not grant Full Access merely because a draft button is missing. Shared-mailbox licensing also depends on features and limits; Microsoft’s shared mailbox guidance does not require a separate mailbox license in every case.

Steps to Use Copilot With the Delegate Mailbox

1. Open the intended mailbox with your own account. Use the mailbox access provided to you. Do not sign in with the owner’s password. Microsoft’s delegate guide explains how mailbox owners authorize delegates and assign folder permissions.
2. Confirm your experience. In Copilot Chat in Outlook, work in the shared/delegated mailbox context and request a draft if the capability is available. The current guide says an additional Copilot configuration or account switch is not required for this support.
3. Review the proposed content. Check facts, confidentiality, recipients, tone, and attachments. Add or verify the authorized signature yourself. A generated message should not be assumed to reproduce the owner’s signature or approval.
4. Review Outlook’s sender field. In the message, show From and choose or enter the owner’s mailbox as appropriate. Microsoft’s send-on-behalf guide describes this workflow for classic Outlook. Other Outlook clients can use different controls. Selecting an address does not confer permission to send from it.
5. Send only after your review. Confirm the result with a test recipient before using the workflow for business mail. Recipients should see the expected sender/delegate relationship.

Common Issues With Copilot and Delegated Sending

If Copilot is unavailable in the mailbox, record Outlook type, version, account, license, mailbox type, and the exact feature. Microsoft’s general Outlook Copilot FAQ still lists primary-mailbox limits for some scenarios, while the newer shared-mailbox Chat guide documents expanded support. Check the relevant experience and rollout rather than assuming every Copilot control works in every client.

If Outlook rejects sending, ask the administrator to verify the actual Send on behalf permission. If the recipient sees only the owner’s name, check whether Send As is also assigned: Exchange uses Send As when both permissions exist. If the signature is wrong, correct the draft; it is not evidence that a hidden Copilot identity setting needs changing.

Send-On-Behalf-Of, Send As, and Full Access Compared

Copilot availability, content quality, and sender authorization are separate checks. Keep all three in the test result, especially when a new mailbox capability is still rolling out.