Outlook Postoffice

We have a Windows workgroup Postoffice that was set up Before I started and I need to change and add some mailboxes however I cannaot find any of the workstations nor on the NT Server the Postoffice administration Icon to set up a new post office. I also don’t know what the master Post office password is. We are able to send and recieve mail now but have to use what account that we have now. Any suggestions on how I can set up a new postoffice?