Removing a Stuck Message from Your Outbox
When you use Microsoft Outlook to send an email, that message should move from the Outbox to the Sent Items queue almost instantaneously. If you notice items in your Outbox queue, that is an indication that something is wrong, and that your email recipients are not getting their messages.
There are a number of things that can cause an email to become stuck in the Outbox queue, but the most common, especially in corporate settings, is a lack of space. Many companies set size restrictions on their user mailboxes, and if you exceed those limits you will not be able to send or receive new mail.
The easiest way to fix this problem is to click on Tools and then Mailbox Cleanup. Use the Mailbox Cleanup tool to find old messages you no longer need and clear up more space. Once that space is cleared, the messages in your Outbox queue should start sending right away. If not you can go into the queue, click on the message and press the Send button. You may want to run the mailbox cleanup tool on a regular basis to keep problems at bay, especially if your corporate policy dictates a maximum size for your Outlook mailbox.