Send & Receive Issues

How to Fix Outlook Send As vs Send on Behalf Mailbox Permissions

Adam Davis Oct 9, 2026 869 views

Question details

The user needs to understand how Outlook handles messages sent from a shared mailbox when an account has both Send As and Send on Behalf permissions, and how to display the sender as acting for the mailbox.

How to Manage Send As and Send on Behalf in Outlook Shared Mailboxes

Product: Microsoft Outlook
Device & OS: not provided
Scenario: Sending an email from a shared mailbox and attempting to choose whether the recipient sees the email as coming directly from the mailbox or on behalf of it.
Observed behavior: When both permissions are assigned, Outlook defaults to Send As, making the message appear to come directly from the shared mailbox without offering a per-message selector.

Before you start

Ensure you have Exchange admin center access or Microsoft 365 administrative privileges, as modifying shared mailbox permissions requires administrator rights.

Solution 1Recommended

Adjust Mailbox Delegation to Force Send on Behalf

Remove the Send As permission from the user account to ensure messages display as being sent on behalf of the shared mailbox.

When both permissions are applied to a user, Outlook prioritizes 'Send As' by default. There is no built-in toggle in the Outlook client to switch between the two on a case-by-case basis.

To make emails explicitly show they are sent on behalf of the mailbox (e.g., 'John Doe on behalf of Support'), the 'Send As' permission must be completely removed from the user's account delegation settings.

Access the Exchange Admin Center

Locate the Shared Mailbox

Go to 'Recipients' and then 'Mailboxes'. Find and select the shared mailbox you need to modify.

Manage Mailbox Delegation

In the mailbox settings pane, select 'Mailbox delegation' or 'Manage mailbox delegation' to view current permission assignments.

Remove Send As Permission

Under the 'Send As' section, locate the specific user and remove their permission. Ensure their account is only listed under the 'Send on behalf' section, then save your changes.

Adjust Mailbox Delegation to Force Send on Behalf

Propagation Delay: Changes to Microsoft 365 and Exchange mailbox permissions can take up to 24 hours to fully propagate and reflect accurately in the Outlook desktop client.

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Frequently Asked Questions

Can I choose between Send As and Send on Behalf for individual emails in Outlook?

No, Outlook does not provide a per-message selector. If an account is assigned both permissions, Outlook automatically defaults to utilizing the 'Send As' permission for all outbound messages from that shared mailbox.

Why does my email show as coming directly from the shared mailbox instead of my name?

This happens because your account has the 'Send As' permission assigned. To display your personal name acting on behalf of the mailbox, an administrator must remove your 'Send As' access while leaving the 'Send on Behalf' permission intact.

How long does it take for shared mailbox permission changes to take effect?

Permission adjustments made in the Microsoft 365 or Exchange admin center typically take a few hours to sync, but can require up to 24 hours to fully propagate to the Outlook desktop client.

Outlook & Email Problems