A customer recently had the problem that e-mails were stuck in the outbox whenever he had just looked at the folder. Was this caused by our Outlook tool ReplyButler? Well, that wasn’t the case (of course 😉 ). But nevertheless it’s a good reason to show 2 solutions to this widespread problem here:
Double-click the e-mail in the outbox, switch to another folder and now submit the e-mail again.
2. Real solution
The only solution to this problem is to disable addins systematically, because one of them causes this problem. You can do that at “File > Options > Add-Ins > Go to: Com-Add-Ins”.
In the customer’s case the problem was caused by the iCloud add-in: