Hi Mohamed,
After updating Office for Mac 2011, the "outbox" has disappeared, but you can see the progress of your mail sending by choosing Window> Progress from the Menu Bar.
For more detailed information, please refer to this thread below:
http://answers.microsoft.com/en-us/mac/forum/macoffice2011-macoutlook/outlook-for-mac-2011-my-outlook-outbox-has/b9e21675-5d1b-4ec8-ab45-4cfb89e35fb8?msgId=ee4be598-d04e-4f27-bac4-f93f2b524f0d
Since this issue is related to Office for Mac, I suggest you send your feedback by clicking Help> Send Feedback in any Office application.
Thanks,
Edward Qu