Delete an Email Stuck in Your Outbox - Outlook 2013
On rare occasions, sending an attachment that exceeds the maximum allowed message size can cause the message to get stuck in your Outbox.
In Outlook 2013 this is unlikely to occur due to a new default 20MB maximum attachment size limit built in to Outlook.
However, if you changed the Windows registry to override the default limit and a message gets stuck in your Outbox, you can follow the step-by-step instructions below to temporarily stop Outlook from trying to send mail. This will allow you to find and delete the message from your Outbox.
Step 2 » Select Advanced from the left-hand side of the Outlook Options window, then Scroll to the Send & Receive heading. Un-check the box labeled "Send immediately when connected". Click OK to close the Outlook Options window.
Step 3 » Close and re-open Outlook in order to stop Outlook from trying to send the email stuck in your Outbox. Select the Outbox for your email account. Locate & delete the message stuck in your mailbox.
Step 4 » From the File menu, select Options and choose Advanced again. Locate the Send & Receive heading and check the box labeled "Send immediately when connected". Click OK to save changes and return to your Inbox.