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Just so that others will have the benefit of this, I am going to add my two centavos to Dave's Answer. If your only problem is that an e-mail is stuck in your Outlook Outbox, it could just be that the size of the e-mai is a problem and Outlook just keeps trying to send it anyway because it can't figure out what is wrong. In that case, simpy disconnect yourself from your network and when you log into MS Outlook do not enter your password. Outlook won't realize that you aren't connected for a few seconds. Then you can open your Out box and right-click and delete the offending e-mail.
If, however, your e-mail is actually being delivered to the recipients but it is still residing in your Out box, it could be that you have somehow mistakenly told Outlook to keep it there.
If this is the case, simply go to Tools | Options | Email Options | and uncheck the box that says IN folders other than the Inbox, save replies with original message.
Now all of your forwarded and replied to mail will go to your Sent Items box.
When this happens to me, usually the first email of the day, I will just open the email in the Outbox folder and press send again.
If that works, then it usually is just a matter of Outlook being closed before an e-mail could be sent, but in the situations listed above, it would not work.
