Viewing Pending Mail for all users
The Wig Administrator program lets you view pending incoming and outgoing messages for all users together. You can do this by selecting Pending Messages for all users from the View menu (or CTRL+M). This will pop up a list of messages:
List of pending INCOMING and OUTGOING messages
You can list all the messages pending for unknown users. Do this by selecting Pending Messages for Unknown from the View menu (or CTRL+U).