Good idea, Beowulf1, and that helped me to force an Outbox, thanks.
But you can keep your Ethernet cable plugged in and simply switch Outlook to Offline mode in the Tools tab while you send yourself the trigger email.
Does anybody else have messages that don't appear in the elusive Outlook 2011 Outbox, but are stuck in a loop uploading from the Outlook Sent folder to iCloud, in order to update the Sent folder on iCloud and other devices?
I had that problem for months, eight emails always uploading. I thought they were still in the Outbox but they weren't, and clicking the cross on the progress bar never worked. I fixed it yesterday. This is what I did, in case this helps anyone else:
1. Compare the Outlook Sent folder to the iCloud Sent folder online to see which messages have not uploaded to iCloud.
2. Select the offending /extra messages in the Outlook > Sent > MobileMe/iCloud folder.
3. If you wish, apply an Outlook Category and colour to them so they are easy to find. You can create a custom category and colour in Categorize > Add New. Then you can quickly view them and work with them as a group by choosing the category in Filters.
4. Copy the messages from the Outlook > Sent > MobileMe or iCloud folder to the Outlook > Sent > On My Computer folder to retain a local copy if you want.
5. Delete the messages from Outlook > Sent > MobileMe or iCloud folder. The loop should stop.
There was probably a fault with the messages (e.g. invalid header or too big). These messages won't appear on Sent mail in iCloud and other devices, but you can forward them to yourself if you need the content on other devices, though they will be new mail in your Inbox rather than in their correct order in Sent, but if it is only a few messages or if it is really bugging you, it might be worth it.
If you want to put them back into iCloud Sent, I was able to do so, with some oddities of order, by this method:
1. Create and name a new folder in the left pane /mailbox folder area of Outlook 2011 on Mac, if that has the mail that needs to be restored to iCloud.
2. Copy the required mail into the new folder.
3. Drag the folder to the Mac desktop, and it will automatically create a .mbox exported file of just that mail. Close or put aside Outlook.
4. Open Mail on the Mac and choose File > Import Mailboxes > Files in mbox format, navigate to choose the file on the desktop and choose Continue to import the messages into Mail. Mail will create a new Import folder containing the folder from Outlook.
5. Open the imported folder to view imported messages.
6. Select an imported message and choose Message > Move to [or Copy to] from the top menu bar and select a destination from the drop down menu, such as Sent.
7. Click on the iCloud destination option that pops up beyond Sent. Mail will show a progress bar for uploading the message to iCloud, and after a minute, depending on file size, it should appear in the corresponding box on iCloud (Sent, in this case), and will then auto load back to the Mail and Outlook boxes (Sent, in this case). Dates should appear correctly on the messages, but their order may be a bit odd.
8. Select subsequent imported messages for the same destination and choose Message > Move [or Copy] Again to iCloud. Not too many at a time, or the upload might get stuck in a loop.
(steps 3—4 from following tips by SallyRF and Scirebroc on another thread at <https://discussions.apple.com/thread/3644627> — thanks to them)
This may be slightly off this thread's Outbox loop topic but I have come back to this thread many times while trying to find a solution for my particular Sent loop, and I haven't found any other information closer to the point, so other people with the same loop will probably read this thread too.