On a computer that is running Windows Vista, some messages may be stuck in the Outbox when you use Windows Mail. You cannot send or delete these messages. Additionally, every time that you close Windows Mail, you are prompted that there are unsent messages in your Outbox.

This problem occurs when the stream entries for the messages are inaccessible before Windows Mail deletes the messages from the Outbox.

Now, you no need to worry about it anymore. Microsoft have release the update to resolved this issue. You may download the update for Windows Vista in 32-bit and 64-bit.