Earlier today, I wrote on the first rule of Word and Outlook email merges – make the email account you will send from your default, and make its corresponding data file (.pst) the default data file too!
The last rule that no one tells you about either is make sure Outlook is open before you send. When Outlook is closed, the messages will send from Word, but won’t leave Outlook. The messages will sit there until you open Outlook and hit the send button!
So the last unspoken rule is open Outlook before you hit the final merge and send button in Word!