How to Save Sent Items in the Original Mailbox for Send As or Send on Behalf (User Mailbox in Microsoft 365)

When a user sends an email as or on behalf of another mailbox in Microsoft 365, Outlook will normally save that sent email in the delegate’s Sent Items folder by default. This means the email may send correctly from the intended mailbox address, but no copy appears in the original mailbox’s Sent Items folder unless the setting is changed. This is normal behaviour for a standard user mailbox. If you want Microsoft 365 to also save a copy of those sent emails in the original mailbox’s Sent Items, you can enable this through Exchange Online PowerShell. For businesses that rely on managed IT services, this is the kind of Microsoft 365 configuration that is usually handled as part of routine administration.

What this guide covers

This guide shows you how to enable sent item copies for a normal licensed user mailbox in Microsoft 365 when someone is sending:

• Send As
• Send on Behalf

This does not apply to shared mailboxes configured through the Microsoft 365 admin portal Sent Items options.

Before you begin

You will need:

• An account with Exchange admin permissions or equivalent Microsoft 365 admin access
• PowerShell on your computer
• The email address of the mailbox you want to update

Important: You must run the command against the mailbox being sent from, not the delegate user’s mailbox. For example, if a staff member is sending from another mailbox, the change must be applied to the mailbox that appears in the From field.

Step 1: Open PowerShell as Administrator

1. Click Start
2. Search for PowerShell
3. Right-click Windows PowerShell or PowerShell
4. Select Run as administrator

Step 2: Install the Exchange Online module

Run the following command:

Install-Module ExchangeOnlineManagement

If prompted to install from PSGallery or approve NuGet, select Yes.

Step 3: Import the Exchange Online module

Run:

Import-Module ExchangeOnlineManagement

Step 4: Connect to Exchange Online

Run:

Connect-ExchangeOnline

A Microsoft sign-in window should appear. Sign in using your Microsoft 365 admin account. If you want to sign in with a specific admin account, you can use:

Connect-ExchangeOnline -UserPrincipalName admin@yourdomain.com

Step 5: Check the current sent item settings

Replace the example email address below with the mailbox you want to update:

Get-Mailbox user@domain.com | Format-List MessageCopyForSentAsEnabled,MessageCopyForSendOnBehalfEnabled

If both values are set to False, the mailbox is currently using the default behaviour.

Step 6: Enable saving copies for Send As

If users send as this mailbox, run:

Set-Mailbox user@domain.com -MessageCopyForSentAsEnabled $true

This enables Microsoft 365 to also save a copy of sent emails in that mailbox’s Sent Items folder.

Step 7: Enable saving copies for Send on Behalf

If users send on behalf of this mailbox, run:

Set-Mailbox user@domain.com -MessageCopyForSendOnBehalfEnabled $true

Step 8: Confirm the change

Run the check again:

Get-Mailbox user@domain.com | Format-List MessageCopyForSentAsEnabled,MessageCopyForSendOnBehalfEnabled

You should now see the relevant setting changed to True.

Step 9: Test the result

After applying the change:

1. Open Outlook as the delegate user
2. Send an email from the original mailbox address
3. Check the delegate’s Sent Items
4. Then check the original mailbox’s Sent Items

A copy should now appear in the original mailbox as well.

Step 10: Disconnect from Exchange Online

When finished, run:

Disconnect-ExchangeOnline

Full command set

You can use the below command block as a full example. Replace the example email address with the mailbox you want to configure:

Install-Module ExchangeOnlineManagement
Import-Module ExchangeOnlineManagement
Connect-ExchangeOnline
Get-Mailbox user@domain.com | Format-List MessageCopyForSentAsEnabled,MessageCopyForSendOnBehalfEnabled
Set-Mailbox user@domain.com -MessageCopyForSentAsEnabled $true
Set-Mailbox user@domain.com -MessageCopyForSendOnBehalfEnabled $true
Get-Mailbox user@domain.com | Format-List MessageCopyForSentAsEnabled,MessageCopyForSendOnBehalfEnabled
Disconnect-ExchangeOnline

If you only need Send As

If users only send as the mailbox, you can use just this command:

Set-Mailbox user@domain.com -MessageCopyForSentAsEnabled $true

If you need to disable it later

You can turn the settings off again using:

Set-Mailbox user@domain.com -MessageCopyForSentAsEnabled $false
Set-Mailbox user@domain.com -MessageCopyForSendOnBehalfEnabled $false

Important note

This setting only changes where sent copies are stored. It does not grant permission for someone to send as the mailbox. The user must already have the correct Send As or Send on Behalf permissions configured separately.

Related service: If your team needs help managing Microsoft 365 securely and efficiently, review our managed IT services.