You're not alone in experiencing this issue. Many users have reported that Outlook becomes unresponsive (shows hourglass) during a mail merge process from Access to Word, especially in recent updates of Microsoft 365 Apps for Business.

This behavior appears to be tied to how Outlook manages background operations and the tight integration among Access, Word, and Outlook during a merge.

What’s Likely Happening

When you initiate a mail merge from Access to Word that involves Outlook (for example, to send emails), Outlook locks certain components to maintain message integrity. This causes the interface to freeze temporarily, preventing you from interacting with it until the merge process finishes.

Why This Might Be a Recent Issue

Recent updates in Microsoft 365 (such as changes in COM object handling or background process security hardening) may have introduced this behavior. Microsoft has been tightening cross-app communication for performance and security, which might be affecting legacy workflows like Access-to-Word merges using Outlook.

Potential Solutions and Workarounds

Run Outlook in a Separate Thread (Different Profile or Instance)

Try launching Outlook separately before starting the merge, and avoid initiating email sending through Outlook during the merge process.

Alternatively, consider using a secondary Outlook profile just for merges, keeping your main profile available for checking email.

Use Delayed Sending or Draft Generation Instead

Instead of sending emails directly during the merge, choose the option to generate email drafts in Outlook.

Once the merge is complete, go into the Drafts folder and review/send them manually. This can reduce the lock on Outlook.

Update Microsoft 365 Apps and Access Runtime

Make sure all Office apps (Access, Word, Outlook) are updated to the latest version. Microsoft might have issued fixes for integration bugs.

Use Office Repair (Control Panel > Programs > Microsoft 365 > Change > Quick Repair) if any components are misbehaving.

Reduce Load During Merge

Try breaking the merge into smaller batches to reduce resource usage.

Avoid running heavy Outlook add-ins during the process.

Check COM Add-ins or Anti-virus Interference

Go to File > Options > Add-ins in Outlook and disable non-essential add-ins to see if it improves responsiveness.

Some antivirus software may interfere with Office automation—temporarily disable it for testing.

Thanks, hope this is helpful.