MacOS - Mail merge issue since word update 16.109 (not corrected with 16.109.1 or 16.109.2)

Question

Dear all, since a couple of weeks, several of our mail merge template have an issue with error box "Unable to route document" at the end of the process. No mail are created/send in Outlook side. Is anybody have the same issue with M365 for business since 16.109 version for MacOS ?

Answer 1

Hi @Eric Jeanniard

Thank you for sharing your concern. 

To ensure I fully understand your situation and provide the most effective assistance, I’ll need a few additional details, such as:  

May I know which Outlook version you are currently using (New Outlook or Legacy Outlook), along with the build number? 

Could you please confirm whether your Microsoft Outlook is set as the default email application on your Mac? 

As far as I know, mail merge functionality tends to be more reliable with Legacy Outlook. You may also consider updating both Word and Outlook to their latest versions to rule out any potential compatibility issues.

Additionally, please verify that both Word and Outlook are signed in with the same Microsoft 365 account, as using different accounts can affect features such as Mail Merge. 

Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution. 

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Answer 2

The behavior matches a MAPI integration problem between Word and Outlook rather than a template corruption issue.

On macOS, Word relies on a MAPI‑compatible email client to complete a mail merge to email. If the default mail client is not fully MAPI‑compatible, Word can complete the merge preview but fail at the final “send” step, which surfaces as errors like “Unable to route document” and no messages appearing in Outlook.

Key points and actions:

1. Ensure a MAPI‑compatible mail client is installed and used
   • For macOS mail merge to email, a MAPI‑compatible client such as Outlook is required.
   • If Outlook is not set as the default mail client, or if another client is intercepting the mail call, Word cannot hand off the merged messages correctly.
2. Use Outlook in a configuration that supports automation/MAPI
   • Similar issues on Windows occur when using New Outlook, which is not fully MAPI‑compliant and therefore cannot reliably send mail‑merge output from Word.
   • While the context here is Windows, the underlying pattern is the same: when the Outlook variant is not MAPI‑compliant, Word completes the merge but no emails are actually sent.
3. Verify the mail merge prerequisites on macOS
   • Confirm that Outlook is installed and configured on the same Microsoft 365 account used in Word.
   • Confirm Outlook is set as the default email program.
   • For macOS, Word explicitly requires a MAPI‑compatible client for bulk email via mail merge.
4. If the issue persists after confirming Outlook configuration
   • Test with a simple new mail‑merge document and a small data source to rule out template‑specific corruption.
   • If the simple test also fails with “Unable to route document,” escalate via Microsoft 365 support, as this points to a regression in the 16.109 Word for Mac build’s integration with Outlook.

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References:

• Use mail merge in Word to send bulk email messages