This is one of the most annoying problems you will experience where a message stucked in Outbox wouldn’t let you delete the stucked message, or send any more messages.
Most problems are fixed by repairing windows live mail through the Control Panel but sometimes, the default repair process doesn’t work.
If you are experiencing the same, here is what you should do.
Download the WMUtil
Close Windows Live Mail
Extract the contents of WMUtil151.zip file and run the exe.
You will see the above menu, click on “Clear Outbox” and wait for the process to finish.
Once done, check your Windows Live Mail again. The stucked message should now be removed.