How to fix the issue.

Please follow the steps outlined below to fix the issue “Email stuck in Outbox while using the Mail merge feature”.

• Close Outlook 2016 completely.
• Open Terminal and run the below commands one by one. Make sure to check the case as it is case sensitive.

1. defaults delete com.microsoft.Outlook
2. killall cfprefsd

• Open the Outlook, check the mail merge and it should be working

please let me know with your comments, If this works or not. I would love to help.