Office Apps Freezing

Fix Word 365 Freezing When Completing a Mail Merge

John Wilson Sep 28, 2026 870 views

Question details

The user needs to resolve an issue where Microsoft Word 365 becomes unresponsive when finalizing a mail merge to send emails via Outlook.

How to Fix Word 365 Freezing When Completing a Mail Merge

Product: Word 365, Outlook
Device & OS: Windows
Scenario: Attempting to send mail merge messages through Outlook using the Finish & Merge feature in Word 365.
Observed behavior: Word 365 completely freezes at the Finish & Merge step, preventing emails from being sent. Standard Office repair and reinstallation do not resolve the issue.

Before you start

Because this solution requires modifying the Windows Registry, please ensure you export a backup of your registry first to prevent accidental system issues.

Solution 1Recommended

Force Classic Outlook via the Registry Editor

Use this method to manually switch back to Classic Outlook if the standard application toggle is missing or unresponsive, resolving the mail merge freeze.

The New Outlook client often struggles with the MAPI requests sent by Word 365 during a mail merge. Forcing the system to use Classic Outlook restores the stable communication channel between the two apps.

Open the Registry Editor

Press the Windows Key + R on your keyboard, type 'regedit' into the Run dialog box, and press Enter.

Navigate to Outlook Preferences

In the Registry Editor address bar, paste or navigate to the following path: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences

Create the UseNewOutlook Value

Right-click on an empty space in the right pane, select 'New' > 'DWORD (32-bit) Value', and name the new entry 'UseNewOutlook'.

Modify the Value Data

Double-click the newly created 'UseNewOutlook' DWORD, change the Value data field to '0', and click 'OK'.

Restart Outlook Processes

Press Ctrl + Shift + Esc to open Task Manager. Locate any running Microsoft Outlook processes, right-click them, and select 'End task'. Finally, reopen Outlook to launch the Classic version.

Force Classic Outlook via the Registry Editor

Registry Caution: Only modify the specific registry key outlined in these steps. Making incorrect changes to other registry keys can cause system instability.

Free Microsoft Office alternative

Experience Stable Document Processing with WPS Office

If Microsoft Word and New Outlook integration issues continue to disrupt your workflow, consider switching to WPS Office. It offers a highly stable environment for document creation and data processing without the heavy resource usage of Office 365.

1. Download and Install: Visit the official WPS website to download the free installation package and install it on your PC.
2. Open Your Documents: Launch WPS Writer and open your existing .docx files without losing any formatting.
3. Utilize Mail Merge: Navigate to the References tab to access the built-in Mail Merge tools and easily link your data sources.

Fully compatible with Microsoft Word (.docx) formatsLightweight application that runs smoothly without freezingIncludes a robust built-in Mail Merge feature for bulk mailingFamiliar user interface requires no learning curve

Frequently Asked Questions

Why does Word 365 freeze during a mail merge?

This is often caused by compatibility issues between Word 365 and the New Outlook client, which currently struggles to process the automated MAPI protocol requests sent by Word during the Finish & Merge process.

Will repairing Microsoft Office fix this mail merge issue?

Typically, no. Because the issue is rooted in the New Outlook application's architecture rather than a corrupted Office installation, standard built-in repair tools usually do not resolve the freezing.

How can I back up the Registry before fixing the Outlook settings?

Open the Registry Editor, click 'File' in the top menu, select 'Export', choose 'All' under the Export range options at the bottom of the window, and save the .reg file to a secure location like your desktop.

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