Mail Merge Attachment Issue - Outlook Programatic access

Question

We are trying to do a mail merge with an attachment.

 

When we send the mail merge, we are getting this popup:

 

 

Even if we allow for 10 minutes, it still asks us to hit allow for each email Outlook sends as seen here:

 

 

If we have 2000 emails, it asks to hit allow 2000 times despite authorizing it for 10 minutes in the last step.

 

I am aware of the Trust Center settings in Outlook for programmatic access but none of the settings are where I can change them, they are kind of greyed out. I followed this suggestion, and it removed the first prompt, but it still asks for each email to hit Allow.

 

 

GPO for Outlook - Microsoft Q&A

 

 

If you send an email mail merge and just use the HTML setting, it works fine, its just the attachment option:

 

 

Microsoft is telling me that this is normal behavior but it would seem odd to me and it wasn't like this a year or so ago.

Answer 1

Hi Steven, 

Thank you for the detailed information and screenshots. 

Based on the behavior you’re seeing, this is related to Outlook’s programmatic access security prompts, rather than a failure of the mail merge itself. 

The key distinction is how Outlook processes different mail merge types: 

• When sending as HTML, Word uses the Outlook object model > this path typically respects Trust Center / Object Model Guard settings. 
• When sending with attachments, Word often uses Simple MAPI instead > this is treated more strictly and triggers separate security prompts. 

This explains why: 

• HTML-only mail merge works without repeated prompts 
• Mail merge with attachments generates a prompt for every message, even after allowing access for 10 minutes 

The prompts shown in the screenshots: 

1. “A program is trying to access email address information…” 
2. “A program is trying to send an email message on your behalf…” 

are expected when Outlook detects programmatic sending via Simple MAPI, which does not fully honor the same Trust Center or Object Model Guard settings. 

Even if the first prompt is suppressed, the per-message send confirmation can still occur, which is why you must click Allow for every email (e.g., 2,000 times). 

Why Trust Center settings are greyed out: 

This typically indicates they are being controlled by Group Policy (GPO), which is expected in managed environments. However, those standard settings alone are not sufficient for this specific scenario. 

Here’s the recommended approach (IT admin action required): 

For trusted internal workflows, the relevant policies to review are the Simple MAPI security prompts, not just Object Model Guard. 

These can be configured via GPO or registry: 

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Security  

Set the following DWORD values: 

PromptSimpleMAPISend = 2  

PromptSimpleMAPINameResolve = 2  

PromptSimpleMAPIOpenMessage = 2  

Value meanings: 

• 0 = AutoDeny 
• 1 = PromptUser 
• 2 = AutoApprove 

 

Please note that disabling these prompts lowers Outlook’s built-in safeguards against unauthorized applications sending emails. Therefore, this change should only be implemented on trusted, managed devices and with approval from your organization’s IT or security team. 

For reference: I get warnings about a program accessing email address information or sending email on my behalf | … 

One extra note:   

• Sending ~2,000 emails with attachments may also be subject to: 
  • Exchange Online sending limits 
  • Anti-spam or throttling policies 
  • Even after suppressing prompts, delivery success is not guaranteed without validating those limits. 

 

I hope this helps clarify what’s happening and why the experience differs from before. If you need further assistance, feel free to reach out. I’m happy to help. 

Thank you again for your patience and understanding. 

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