How to apply a personal signature to an email sent from a shared mailbox

Scenario

Users send emails from a shared mailbox, but would like to be able to apply a personal signature to some emails.

Resolution

To apply personal signatures to emails sent from shared mailboxes: 

To apply a personal signature using client-side:

1. Enable Client-Side signatures.
   
   
2. Install the Exclaimer Outlook Add-in. For more information, see how to Install the Outlook Add-in.
   
   
   We recommend: If you are using an Outlook version older than 2019 or an On-Premise mailbox, then install the Exclaimer Signature Update Agent. For more information, see how to install the Exclaimer Signature Update Agent (Windows). You can access the latest version for deployment from here: Exclaimer Signature.
   
   
3. Synchronize your signature with Exclaimer to ensure that the updated signature is applied to the email messages. For more information, see How to synchronize user contact details for Microsoft 365 subscription.
   
   
4. Open Outlook and select New Email.
   
   
5. Open the Add-in from the Outlook toolbar.
   
   
6. Change the From address.
   
   
   _{Change the From address} 
   
   
7. In the Add-in pane, select the main account.
   
   
   _{Select the main email account}
   
   The drop-down list is enabled only when the current sender and the logged in sender email addresses are different.
   
   NOTE: You can add your own signature when sending an email from a Shared Mailbox using Outlook Add-in only when the selected sender (From address) is on the same Microsoft 365 tenancy.
8. Select the appropriate signature for the main account.

To apply a personal signature using server-side (Microsoft 365 only):

In the Exchange admin center:

1. Sign in to the Exchange admin center as an Administrator.
   
   The Exchange admin center is displayed.
   
   
2. From the menu sidebar, select Recipient then select Mailbox. 
   
   
3. Select the mailbox you wish to view the delegated permissions. 
   
   
4. In the details pane, select the Delegation tab. The Send as and Send as behalf permissions are displayed.
   
   
5. Select the Send on Behalf permission to allow users to send emails from the shared mailbox on behalf of their personal account.

In Exclaimer:

1. Disable the Send on Behalf setting in the Manage Mail Flow screen.