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How to Set Up Send As and Send on Behalf Permissions in Exchange Online

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Who This Affects and What It Fixes

This guide is for small-business employees who need to allow one person to send email messages as another email address, or on behalf of another email address. Both options are available for shared mailboxes and individual active user mailboxes inside the Microsoft 365 admin center. If your organization needs either type of delegation set up, follow the steps below or contact ACS for assistance.

What You Will Need

Before you begin, make sure you have administrator access to your Microsoft 365 admin center and know which mailbox (shared mailbox or active user) you want to configure, as well as which person should receive the permission.

Steps to Grant Send As or Send on Behalf Permissions

  1. Sign in to your Microsoft 365 admin center.
  2. In the left navigation, go to either Groups > Shared mailboxes if you are working with a shared mailbox, or Users > Active users if you are working with an individual user’s mailbox.
  3. Click the row that contains the shared mailbox or the active user you want to configure.

  4. A slideout panel will appear on the right side of the screen. Depending on where you navigated:

    • If you are in Active users: Click the Mail tab. Locate the Mailbox permissions heading. From there, select either Send as or Send on behalf and add the person who should have that permission.
    • If you are in Shared mailboxes: Locate the Manage mailbox permissions heading. From there, select either Send as or Send on behalf and add the person who should have that permission.
  5. Save your changes.
  6. Test by having the person you granted access to send a message using the delegated address, and verify that it arrives correctly.

Send As vs. Send on Behalf: What Is the Difference?

Send As makes the email appear as if it came directly from the other address — the recipient will not see the sender’s own address at all. Send on Behalf shows the recipient that the message was sent by one person on behalf of another address, so both names are visible. Choose the option that matches what your organization requires.

Need Help?

If you run into trouble or are unsure which permission type is right for your situation, contact the ACS support team for guidance.

Common questions

What is the difference between Send As and Send on Behalf in Exchange Online?

Send As makes the email appear to come entirely from the other address, with no indication of who actually sent it. Send on Behalf shows the recipient that the message was sent by one person on behalf of another, so both addresses are visible in the email.

Can I set up Send As or Send on Behalf permissions for both shared mailboxes and regular user mailboxes?

Yes. In the Microsoft 365 admin center you can configure these permissions for shared mailboxes under Groups > Shared mailboxes, or for individual users under Users > Active users.

How do I confirm that the Send As or Send on Behalf permission is working?

After saving the permission, have the person you granted access send a test email using the delegated address and verify that it is received correctly by the intended recipient.