I have an App that does mass emails. It uses a spreadsheet with an email column to accomplish this. It works fine except for...

After some varying amounts of emails have been sent the Outbox folder starts filling up. The App continues to run until it is done.

If we go to Outlook and press send/receive nothing happens.
If we close Outlook and exit without sending it Looks like Outlook has quit, but you can't restart it until you use Task Manager to kill the Outlook Task.

Upon restarting outlook sends the remainder of the emails.

What am I doing wrong?