I’ve done a few dozen installs of the new office 2013 on various machines lately and until now all email hosting has been through either gmail or 0ffice365 so I hadn’t come across the issue of messages being stuck in the outbox.

In my case the email account in question was an IMAP account and no matter what I did I was unable to stop messages being in the outbox. They were still sending, just also leaving a copy in the outbox and you couldn’t delete them.

There are quite a few possible solutions but the none of them seemed to fit my cause. 

Fix

After all my searching and trying a whole bunch of settings it was quite an easy fix. It’s something I should have tried but because I hadn’t used IMAP accounts in a while I just plain forgot.

Open up the account settings > Change > Advanced

Then under root path add ‘inbox’ save your settings and close them and you are good to go.Well I was! I hope this helps someone.