Mail Merge is a long‑standing Microsoft Office feature that enables users to send personalized emails, letters, labels, and documents to large recipient lists with minimal manual work. This article consolidates guidance, tutorials, known issues, and helpful resources to streamline Mail Merge—especially when sending through Outlook Classic. 

1. Overview

Mail Merge integrates Microsoft Word, Excel, and Outlook to generate individualized messages at scale. It is commonly used for:

• Bulk but personalized announcements
• Follow‑up communications
• Notifications
• Documents with variable data fields

Microsoft’s official documentation provides a general walkthrough of using Word to produce personalized email, letters, labels, envelopes, and more.

Methods

Method 1: Temporarily Set Shared Mailbox as Default

1. Open Outlook and go to File > Account Settings > Account Settings.

2. In the Email tab, select the shared mailbox account.

3. Click Set as Default.

4. Restart Outlook to apply the change.

5. Run your Word mail merge; emails will now send from the shared mailbox.

6. After sending, repeat steps to set your original account back as default.

It does not rely on external sources—just standard Outlook steps—so no citations are needed.

Method 2: Create a New Outlook Profile Configured Only With the Shared Mailbox

If Outlook continues sending Mail Merge messages from the wrong account, the most reliable fix is to create a dedicated Outlook profile that contains only the shared mailbox. Word will always send Mail Merge emails using the default account in the selected profile.

Steps

1. Close Outlook completely.

2. Open the Outlook Profile Manager:

   • Press Windows Key + R
   • Type: control mlcfg32.cpl
   • Press Enter
     (Alternatively: Control Panel → Mail → Show Profiles)

3. Create a new profile:

   • Click Add…
   • Enter a name such as SharedMailbox‑Merge
   • Click OK

4. Add only the shared mailbox:

   • When prompted for the email account, enter the shared mailbox address.
   • Complete the setup wizard.
   • Do not add any other mailbox or personal account.

5. Set the new profile as the default:

   • In Mail Profiles, select Always use this profile
   • Choose your new SharedMailbox‑Merge profile from the dropdown
   • Click Apply → OK

6. Open Outlook using the new profile.

   • Outlook may appear to fail during first‑time configuration—this is normal.
   • Continue anyway and allow Outlook to finish initializing.

7. Run your Word Mail Merge.

   • Word will now send all merge emails from the shared mailbox, since it is the only account in the profile.

8. (Optional) Switch back after sending:

   • Return to Mail → Show Profiles
   • Set your normal profile as the default again.

2. Sending Mail Merge from a Shared Mailbox

If messages need to originate from a shared mailbox, Outlook must be configured properly:

• The shared mailbox must be the only account in the Outlook profile.
• When creating a profile, Outlook may appear to “fail.” Often, you can continue, open Outlook anyway, and then set the new profile as default.
• If Outlook continues to send from the wrong account, a registry fix such as NewItemsUseDefaultSendingAccount-2013.reg can force Outlook to always use the default sending account. 

This resolves the common situation where Outlook chooses the wrong account due to profile or data‑file priority issues.

3. Known Issues: Wrong Account Used When Sending

Outlook sometimes sends Mail Merge emails from the account associated with the default data file, not the account the user selected as the default mail account. This behavior has been documented for many versions of Outlook (2010, 2013, 2016, and Classic Outlook). 

Workarounds include:

• Rebuilding the Outlook profile
• Using the registry fix noted above
• Ensuring the desired account's data file is set as primary

4. Summary

Mail Merge remains a powerful tool for delivering personalized high‑volume messages in Outlook Classic. Key considerations include:

• Correct Outlook profile configuration—especially with shared mailboxes
• Understanding default account behavior and possible inconsistencies