I noticed a while ago that my Outlook 2010 connected over IMAP to my company email and Outlook Connector for MSN to my personal Hotmail account was always in the process of trying to send messages – even when I hadn’t written a message. This started causing more problems as things would sit in my Outbox rather than going, so I decided yesterday to get to the bottom of it.
I found this post which explained that it could be an old read receipt. I downloaded the tool referenced in there and ran it but didn’t find any read receipts – but did find two old email messages sitting in outbox for a Personal Folders file (not the default PST as the post mentions – that one was empty, but there was another one that had messages sitting in it). Deleting those as described in the post (admittedly a rather geeky process that involves using this tool to call specific MAPI APIs, but it’s well outlined in the blog post how to do this) fixed the problem.
There is a $50 tool called OutlookSpy (with a free 30-day trial) that was also mentioned and might help some folks who find the tool I used a bit too geeky.