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Personal signature not available when using a shared mailbox in Classic Outlook

  1. Exclaimer Knowledge Base
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Payal Arya
  • Updated

Scenario

When using the Exclaimer Outlook Add-in in Classic Outlook, the signature switcher drop-down may not be available when composing an email from a shared mailbox.

The Add-in pane may display No signatures or only show signatures associated with the shared mailbox, with no option to switch to a personal signature.

Reason

This behavior occurs when you have added the shared mailbox to Classic Outlook as a full, separate account (via File > Account Settings) rather than as a delegated mailbox under the user’s primary account.

When configured as a separate account, Classic Outlook handles the shared mailbox differently. As a result, the Exclaimer Outlook Add-in cannot detect the change of sender required to display the signature switcher.

For the signature switcher to work as expected, configure the shared mailbox as a delegated mailbox under the user's primary Outlook account.

Resolution

To use the Exclaimer signature switcher with a shared mailbox in Classic Outlook, add the shared mailbox as a delegated mailbox under the user's primary account, rather than configuring it as a separate Outlook account.

There are two supported methods:

Option 1: Re-enable Exchange automapping

When a user is granted Full Access permission to a shared mailbox in Microsoft 365, Exchange automapping is enabled by default. This automatically adds the shared mailbox under the user’s primary account in Classic Outlook.

If you have disabled automapping, you can re-enable it using Exchange Online PowerShell.

NOTE: To change the automapping setting, you must first remove the existing Full Access permission and then add it again with automapping enabled. For more information, see the Microsoft Learn article Remove automapping for a shared mailbox.

Run the following commands in Exchange Online PowerShell:

  1. Connect-ExchangeOnline
  2. Remove-MailboxPermission -Identity <sharedmailbox@domain.com> -User <user@domain.com> -AccessRights FullAccess 
  3. Add-MailboxPermission -Identity <sharedmailbox@domain.com> -User <user@domain.com> -AccessRights FullAccess -AutoMapping $true

After you apply the change, restart Outlook.

With automapping enabled, the shared mailbox is added under the user's primary account rather than being configured as a separate Outlook account. Automapping mounts the shared mailbox under the user's primary account rather than creating a separate OST file for it.

Option 2: Add the shared mailbox through Exchange account settings

If you cannot use automapping, you can manually add the shared mailbox under the user's primary account in Classic Outlook.
To do this:

  1. In Classic Outlook, navigate to the File menu, select Account Settings, then select Account Settings.
  2. Select the user's primary email account, then select Change.
  3. Select More Settings, then open the Advanced tab.
  4. Under Open these additional mailboxes, select Add.
  5. Enter the shared mailbox email address and select OK.
  6. Select OK, then Next, then Finish.
  7. Restart Outlook.

The shared mailbox should now appear under the user's primary account rather than as a separate top-level account.

NOTE: This configuration does not create a separate OST file for the shared mailbox. If a separate OST file is required for the shared mailbox, the Exclaimer signature switcher is not supported for this configuration in Classic Outlook.
Test after re-adding the shared mailbox

Before you test the signature switcher, check the following:

  • The user has Send As or Send on Behalf permissions for the shared mailbox in Microsoft 365.
  • The Senders list for the relevant Exclaimer signature includes the shared mailbox.
  • If the shared mailbox account has Sign-in blocked enabled, enable Synchronize Disabled Accounts in Exclaimer.

Once configured, compose a new email, change the From address to the shared mailbox, and open the Exclaimer Add-in pane. The signature switcher should now be available.

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