Copilot in Outlook With Send From Alias: Identity Selection Logic

When you use Copilot in Outlook to draft an email and you have multiple aliases configured on your mailbox, the identity Copilot uses to send the email can be confusing. You might expect Copilot to always use your primary email address, but the logic depends on where you started the draft and which alias is currently selected in the From field. This article explains the exact selection logic Copilot follows when deciding which identity to use for sending, how the Send From Alias feature interacts with Copilot drafts, and what you need to check before you click Send.

Microsoft 365 users who manage shared mailboxes or have multiple SMTP aliases on their primary mailbox often encounter unexpected sender addresses in Copilot-generated emails. The root cause is that Copilot does not automatically default to your primary alias. Instead, it inherits the From address that was active when you opened the Copilot pane or started a new message. Understanding this inheritance pattern helps you avoid sending from the wrong identity.

This article covers the identity selection rules for Copilot in Outlook on Windows, Outlook on the web, and new Outlook for Mac. It also explains how to override the default behavior and what happens when you use a shared mailbox or a group alias.

Identity Selection Logic: How Copilot Chooses the Sender Address

Copilot in Outlook uses a straightforward inheritance model for determining the sender address. It does not scan your mailbox aliases or make a decision based on the recipient domain. The logic is tied to the state of the message compose window at the moment you click the Copilot button or invoke the Copilot draft command.

Primary Alias vs Selected Alias

Every Microsoft 365 mailbox has a primary SMTP address. This is the address listed first in the Exchange Online proxyAddresses attribute. When you open a new email message in Outlook, the default From address is your primary SMTP address unless you have manually changed it in a previous session or set a different default in Outlook settings.

If you have added additional aliases to your mailbox, you can select any of them from the From dropdown in the message header. Copilot reads the current From field value at the time of generation. It does not store a preference or remember which alias you used last. The rule is simple: the address visible in the From field when you press the Copilot button is the address Copilot uses for the draft.

How Shared Mailboxes Affect the Logic

For shared mailboxes, the behavior is identical but has an extra prerequisite. You must have full access and send-as permissions on the shared mailbox. When you open a new message and select the shared mailbox from the From dropdown, Copilot uses that shared mailbox address. If you do not select the shared mailbox first, Copilot uses your primary mailbox address even if you are a member of the shared mailbox.

What Happens When You Change the From Address After Generation

After Copilot generates the draft, you can manually edit the body or subject. However, changing the From address after generation does not retroactively update the identity Copilot used for drafting. The draft text itself is not tied to the sender address, but the system metadata that records the sender is fixed at generation time. If you switch the From address after generation and then click Send, the email goes out from the new address you selected, not the one Copilot used. This is because Outlook re-evaluates the From field at send time, not at draft time.

This means you can override Copilot’s identity selection by changing the From field before sending. The draft content remains unchanged, but the sender address is whatever you set in the header.

Steps to Control Which Identity Copilot Uses for Drafts

Follow these steps to ensure Copilot sends from the alias or mailbox you intend.

1. Open a new email message in Outlook
   Press Ctrl+N on Windows or Cmd+N on Mac to open a new message window. Do not start typing in the body yet.
2. Select the correct From address before opening Copilot
   In the message header, click the From button. If you do not see the From field, go to Options > Show From. Select the alias, shared mailbox, or group address you want Copilot to use. The address you select here is the one Copilot will use for generation.
3. Open Copilot and generate the draft
   Click the Copilot icon in the ribbon or press Alt+I to open the Copilot pane. Enter your prompt and click Generate. Copilot writes the draft using the From address you selected in step 2.
4. Verify the From address before sending
   After Copilot finishes the draft, check the From field again. If you need to send from a different address, change it now. The draft content stays the same, but the sender address updates to the new selection.
5. Send the email
   Click Send. The recipient sees the address you had in the From field at the moment you clicked Send, not the address Copilot used during generation.

Common Mistakes and Things to Avoid With Copilot and Aliases

Copilot Drafts From Your Primary Address Even Though You Have Aliases

This happens when you open Copilot before selecting an alias. The default From address is your primary SMTP address. To fix this, always select the alias in the From field before clicking the Copilot button. If you already generated the draft, delete it, select the correct alias, and regenerate.

Copilot Shows a Shared Mailbox Address, but the Recipient Sees Your Primary Address

This can occur if you have send-as permissions on the shared mailbox but the From field was not set to the shared mailbox at generation time. Copilot might display the shared mailbox name in the draft header, but the actual sender address in the sent message is the one from the From field at send time. Always verify the From field immediately before sending.

Changing the From Address After Generation Causes the Draft to Reset

In some versions of Outlook, switching the From address after Copilot generates the draft triggers a warning or resets the Copilot-generated content. If this happens, you must regenerate the draft after selecting the correct alias. To avoid this, select the alias before generating the draft.

Copilot Identity Selection: Primary Alias vs Selected Alias vs Shared Mailbox

Scenario	From Address at Generation Time	From Address at Send Time	Result for Recipient
New message, no alias selected	Primary SMTP address	Primary SMTP address	Primary address shown
Alias selected before Copilot generation	Selected alias	Selected alias	Selected alias shown
Alias selected after Copilot generation	Primary SMTP address	New alias selected after generation	New alias shown
Shared mailbox selected before Copilot generation	Shared mailbox address	Shared mailbox address	Shared mailbox address shown
Shared mailbox selected after Copilot generation	Primary SMTP address	Shared mailbox address	Shared mailbox address shown

Copilot in Outlook uses the From address that is active at the moment of generation for its internal processing. However, the final sender address is always the one in the From field when you click Send. This dual-check system means you have full control over the sender identity even if Copilot initially used a different address.

To avoid confusion, make it a habit to set the From field before opening Copilot. If you manage multiple aliases or shared mailboxes, create a quick checklist: select the address, generate the draft, verify the address, then send. This workflow eliminates the risk of sending from the wrong identity.

For advanced users, consider using Outlook Quick Steps or Power Automate flows to pre-set the From address based on the recipient domain or subject keywords. This automation ensures Copilot always drafts from the correct alias without manual selection each time.