The process by which information stored in Microsoft Mail 3.x mail systems is replicated between postoffices. There is only one directory server postoffice in a Microsoft Mail 3. x mail system; other postoffices that participate in directory synchronization are called requestor postoffices.
Requestor postoffices send their address list updates to the directory server postoffice, which then sends cumulative changes back to the requestor postoffice.
Directory synchronization also ensures that the global address list is updated.