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: