Microsoft Word's mail merge feature only sends emails from Outlook's default email. This article instructs how to add a shared mailbox to Outlook and set it as the default email so the mail merge will send emails from the shared mailbox instead.

Add the Shared Mailbox to Outlook

1. Open the Outlook Application
2. Click File on the top toolbar
3. Click the Account Settings button, and select Account Settings from the dropdown
4. Click the New button above the list of email addresses
5. Enter the shared email address into the box and click connect.
6. Click sign-in with another account
7. Enter your email address and click Next
8. Enter your password and click Sign In
9. Once signed in, click done, exit out of all open Outlook windows, and reopen Outlook. You’ll now see the shared inbox in the left-hand navigation pane.

Set the Shared Email as the Default Email to Send As

1. Click File on the top toolbar
2. Click Options in the bottom left corner of Outlook
3. Select Mail from the options on the left side of the Outlook Options window
4. Scroll to the Send Messages section and check the box for Always use the default account when composing new messages, then click Ok
5. Click file on the top toolbar again
6. Click the Account Settings button and select Account Settings from the dropdown
7. Select the shared email address from the list, and click Set as Default

Once the mail merge is sent, be sure to change your email back to the default by following steps 5-7 above to ensure future emails you send aren't sent as the mailbox.