How To Send On Behalf Outlook: Complete Step-by-Step Guide

Sending emails "On Behalf Of" in Microsoft Outlook requires proper delegation permissions configured within the Exchange Admin Center or Microsoft 365 admin portal before you can draft and transmit messages displaying another user or shared mailbox name. This comprehensive guide covers permission configurations, desktop and web client execution, and technical troubleshooting to ensure your delegated messaging workflow functions seamlessly.

Essential Prerequisites and Permission Setup

Before configuring your Outlook interface to send emails on behalf of another user or shared mailbox, administrative permissions must be established at the tenant or server level. Without explicit delegate rights assigned through directory services, Exchange Server or Exchange Online will reject the transmission with a non-delivery report (NDR) error code.

• Essential Tools & Access: Global Administrator, Exchange Administrator rights, or Full Access / Send As permissions on the target mailbox. Microsoft 365 Business Standard, Enterprise, or Exchange Online plan required.
• Mandatory Standards & Knowledge: Familiarity with Active Directory object properties, SMTP header standards, and Exchange Role-Based Access Control (RBAC).
• Time & Scope Benchmarks: Permission propagation takes between 15 to 60 minutes across cloud clusters. Desktop client synchronization typically requires restarting the Outlook application.

Step-by-Step Execution for Outlook Desktop and Web Clients

Step 1: Verify and Configure Delegate Permissions in the Exchange Admin Center

• Log in to the Microsoft 365 admin center using administrator credentials and navigate to the Exchange admin center dashboard.
• Select recipients from the left-hand navigation menu, choose mailboxes, and click on the specific user mailbox or shared mailbox you intend to send on behalf of.
• Click on the delegation tab within the mailbox properties pane and locate the "Read and manage (Full Access)" and "Send as" permission settings.
• Click edit to add your user account to the list of authorized delegates, then save the changes to update the directory database.

Pro-Tip: If you only require the ability to send messages that display the owner's name without managing their inbox contents, ensure you are granted explicit "Send on Behalf" permissions rather than full mailbox access to maintain recipient privacy.

Step 2: Unhide and Display the From Field in Outlook Desktop Client

• Open Microsoft Outlook on your Windows or macOS workstation and click on the New Email button to open the message composition window.
• Locate the ribbon menu at the top of the blank message window and click on the Options tab.
• Click on the "From" button within the Show Fields group to toggle the From field visibility directly above the To line in your message header.
• Click on the displayed From button within your draft message, select "Other Email Address" from the drop-down menu, and enter or search for the address of the mailbox you are authorized to represent.

Warning: Do not type the delegated email address manually into the From field if it has not been cached in your local Offline Address Book (OAB), as this will trigger an immediate permission validation failure upon sending.

Step 3: Send on Behalf Using Outlook on the Web (OWA)

• Open your web browser, navigate to Outlook on the web, and log in with your primary enterprise credentials.
• Click the New Message button to open a blank composition pane in the reading view or a separate browser window.
• Click the three horizontal dots (More options) menu icon located at the top of the composition pane and select "Show From" from the available options.
• Click on your own name displayed in the newly appeared From field, clear it, and type the target shared mailbox or user address. Select the correct matching entry populated from the global address list.
• Compose your message body, add required attachments, and click the Send button to dispatch the email with the dual-identity header.

Comparison of Outlook Delegation Methods and Permissions

Common Configuration Failures and Field Fixes

• Root Cause: The Offline Address Book (OAB) on your local machine is outdated, causing Outlook to fail resolving the delegated mailbox identity.
  
  
  • Actionable Fix: Go to the Send / Receive tab in the Outlook ribbon, click Send/Receive Groups, and select Download Address Book to force-synchronize your client with the server directory.
• Root Cause: Lack of explicit "Send on Behalf" or "Send As" permissions assigned in the Exchange Admin Center.
  
  
  • Actionable Fix: Contact your system administrator to verify that your user principal name (UPN) is explicitly added to the delegation list of the target mailbox properties.
• Root Cause: Cached credentials or token expiration within the Outlook session preventing authorization validation.
  
  
  • Actionable Fix: Sign out of your Microsoft 365 account entirely, restart the Outlook desktop client, and re-authenticate with your primary enterprise credentials.

Frequently Asked Questions

Why does the recipient see "on behalf of" in the email header?

When you send a message using the Send on Behalf permission, Exchange stamps both your sender identity and the mailbox owner's identity into the SMTP headers. This transparent labeling informs the recipient that the email was composed and transmitted by a delegate rather than the primary account holder.

Can I send on behalf of a shared mailbox without admin assistance?

If the shared mailbox has been configured with the "Delegation" option allowing self-service additions, you can add yourself through Outlook settings. Otherwise, administrative intervention via the Microsoft 365 or Exchange admin center is mandatory to comply with organizational security policies.

How do I reply from a shared mailbox by default in Outlook?

Open Outlook on the web, navigate to Settings, select Mail, and locate the "Message reply" or "Default reply address" section. Configure your preferences to always send replies from the address that received the message, or manually select the From field for each individual outgoing thread.

What is the difference between Send As and Send on Behalf?

The Send As permission masks the sender entirely, making the outgoing email appear as if it originated directly from the shared mailbox or target user without mentioning your name. Send on Behalf explicitly displays your name alongside the owner's name in the message header, preserving audit transparency.

Why is the From button missing in my Outlook composition window?

The From field is hidden by default in Microsoft Outlook to minimize interface clutter for single-user accounts. You can permanently enable it for all future messages by accessing the Options tab in any blank composition window and toggling the From visibility checkbox.

Streamline your organizational communications and eliminate email delivery errors by establishing robust mailbox delegation workflows today.