Delete an Email Stuck in Your Outbox - Outlook 2003 & 2007
If you attempt to send an email with an attachment larger than the maximum size allowed, the message may get "stuck" in your Outbox. Follow the step-by-step instructions outlined below to temporarily disable Outlook 2003 & 2007 from sending an email. This will allow you to locate and remove the message from your Outbox. Note: You may need to force-quit Outlook and restart your computer before updating your settings.
From the Tools menu at the top of the screen, select Options
Select the Mail Setup tab and click the Send/Receive button
Be sure the All Accounts option is selected and click the Edit button
Un-check the box labeled 'Send mail items'
Click 'Close' to close the Send/Receive Groups window
Click OK to close the Options window
Shut down Outlook
Re-open the program and click on your Outbox folder
Select and delete email(s) with oversized attachments
Repeat steps 2-8 (Note: On Step 5, re-check the box labeled 'Send mail items' to restore original settings)
Outlook 2010 & 2013 users click here for updated instructions.