How to Add a Delegated Mailbox With Full Access in Outlook

You need to access another person’s mailbox in Outlook because they granted you full access permissions. Full access allows you to read, create, and delete items in that mailbox as if it were your own. This article explains how to add a delegated mailbox with full access using two methods: Auto Mapping and manual configuration. You will learn the exact steps for both Outlook for Microsoft 365 and Outlook 2019, 2016, and 2013.

What Is a Delegated Mailbox With Full Access

A delegated mailbox is another user’s mailbox you can manage without needing their password. Full access permission grants you the ability to read, create, modify, and delete all items in that mailbox. This permission is assigned by an Exchange administrator or the mailbox owner using the Exchange Admin Center or PowerShell. The feature is commonly used by administrative assistants, team leads, and IT staff who need to manage shared or executive mailboxes.

Before you begin, confirm that you have been granted Full Access permission. Your Exchange administrator must assign this permission to your user account. You also need Outlook configured with your own mailbox. Outlook will either automatically detect the delegated mailbox or require manual addition depending on your Exchange server version and settings.

Auto Mapping Explained

Auto Mapping is an Exchange feature that automatically adds mailboxes to your Outlook profile when you have Full Access permission. It works with Exchange Online and Exchange Server 2013, 2016, and 2019. When you open Outlook, the delegated mailbox appears in the folder pane under your own mailbox. No manual steps are needed. If the mailbox does not appear, Auto Mapping may be disabled or your Exchange server version may not support it.

Method 1: Add a Delegated Mailbox Using Auto Mapping

This method works if your Exchange administrator has granted you Full Access and Auto Mapping is enabled. Follow these steps to add the delegated mailbox to Outlook.

1. Close Outlook completely
   Ensure Outlook is not running. Auto Mapping occurs when Outlook starts and connects to the Exchange server.
2. Open Outlook
   Launch Outlook. Wait for it to fully synchronize with the Exchange server. This may take up to 60 seconds.
3. Check the folder pane
   Look in the left navigation pane. The delegated mailbox appears below your own mailbox with the name of the mailbox owner. The mailbox name is usually the display name of the user who granted you access.
4. Expand the mailbox
   Click the arrow next to the mailbox name to expand its folders. You can now access Inbox, Sent Items, Calendar, and other folders.

If the delegated mailbox does not appear, proceed to Method 2.

Method 2: Add a Delegated Mailbox Manually

Use this method when Auto Mapping does not work, is disabled, or you are using an older Exchange server version such as Exchange 2010. You can also use this method to add a mailbox that you already have permission to access but is not automatically appearing.

1. Open Account Settings
   In Outlook, click File in the top-left corner. Click Account Settings and then Account Settings again from the dropdown menu.
2. Select your Exchange account
   In the Account Settings dialog, click the Email tab. Select your Exchange or Microsoft 365 account and click Change.
3. Open More Settings
   In the Change Account dialog, click More Settings in the bottom-right corner.
4. Go to the Advanced tab
   In the Microsoft Exchange dialog, click the Advanced tab.
5. Click Add
   Under the section Open these additional mailboxes, click Add.
6. Enter the mailbox name
   Type the name of the mailbox you want to add. This is the display name of the user whose mailbox you have permission to access. Click OK.
7. Confirm the mailbox appears
   The mailbox name now appears in the list under Open these additional mailboxes. Click OK to close the Microsoft Exchange dialog.
8. Finish the setup
   Click Next in the Change Account dialog, then click Finish. Click Close in the Account Settings dialog.
9. Restart Outlook
   Close and reopen Outlook. The delegated mailbox now appears in the folder pane.

Issues After Adding a Delegated Mailbox

Delegated Mailbox Does Not Appear After Manual Addition

If the mailbox still does not appear after restarting Outlook, verify that you have Full Access permission. Contact your Exchange administrator to confirm the permission is assigned to your user account. Also check that you typed the mailbox name correctly. If the name is misspelled, Outlook cannot find the mailbox on the Exchange server.

Outlook Prompts for Credentials When Opening the Delegated Mailbox

This occurs when your cached credentials are outdated or the Exchange server requires reauthentication. Close Outlook and open the Credential Manager in Windows. Go to Control Panel > User Accounts > Credential Manager. Under Windows Credentials, remove any entries related to Outlook or Microsoft Office. Restart Outlook and enter your credentials when prompted.

Delayed Synchronization of the Delegated Mailbox

A newly added delegated mailbox may take several minutes to synchronize for the first time. The synchronization speed depends on the size of the mailbox and the network connection. Wait 5 to 10 minutes. If items still do not appear, check that your Outlook is set to Cached Exchange Mode. Go to File > Account Settings > Account Settings > select your account > Change. Ensure the Use Cached Exchange Mode checkbox is selected. Slider settings can also affect sync speed.

Cannot Send Emails From the Delegated Mailbox

Full Access permission allows you to read and manage mailbox content, but it does not automatically grant Send As permission. To send emails from the delegated mailbox, you need Send As or Send on Behalf permission. Contact your Exchange administrator to assign the appropriate send permission. Once granted, you can change the From field in a new email to the delegated mailbox address.

Adding a Delegated Mailbox in Outlook: Auto Mapping vs Manual Method

Item	Auto Mapping	Manual Method
Setup effort	No user action required	Requires account settings changes
Exchange version support	Exchange Online, Exchange 2013 or later	All Exchange versions
Outlook restart needed	Yes, to trigger Auto Mapping	Yes, after manual addition
Permission requirement	Full Access only	Full Access only
Reliability	Dependent on Auto Mapping being enabled	Works even when Auto Mapping is disabled

You can now add any delegated mailbox with full access using either Auto Mapping or manual configuration. If the mailbox still does not appear, verify your permissions with your Exchange administrator. Try using Outlook Web App to add the mailbox from Settings > View all Outlook settings > Mail > Sync email. This often triggers Auto Mapping in the desktop client. For advanced control, ask your administrator to enable or disable Auto Mapping using the Set-Mailbox PowerShell cmdlet with the -Automapping parameter.