If you are using Outlook for Mac, use the following methods to delete messages stuck in your Outbox.
When the message is stuck because it has a large attachment, the Outbox should be visible in the folder list.
- Right click on message in Outbox, choose Open Message
- Remove the attachment
- Press Send
This will re-send the message without the over-sized attachment. If you don't want to send the message, delete it from the outbox instead of removing the attachment.
If the Outbox is not visible, and you use Outlook 2016 for Mac, start a Send and Receive then:
- Open the Sync Status dialog (1)
- Either click the Stop Sync button (2) in the lower left or the little x at the right of the entry to stop the send and receive.
- Once you stop the send and receive, the Outbox will be visible (3) in the folder list.
If you use Outlook 2011 and don't want to send the message or its stuck for other reason:
- Close Outlook 2011
- Hold the Shift key down while reopening Outlook.
- Go to Outbox and delete the stuck message.
If the Outbox is not visible, initiate a send and receive and open the Progress dialog. Either click the Stop Sync button in the lower left or the little x at the right of the entry to stop the send and receive. The Outbox should now be visible in message list and you can remove the attachments or delete the message.