Certain applications, such as a directory synchronization service, need to retrieve incremental changes from the Microsoft Exchange Server directory. This is done through the use of the following operational attributes, which exist on every object in the Microsoft Exchange Server directory:
| Attribute | Description |
| USN-Changed | Integer incremented by the Microsoft Exchange Server directory every time a modification is made to an object (deletions treated as any other modification to the object) |
| USN-Created | Integer that represents when an object was created in the Microsoft Exchange Server directory |
| When-Changed | UTC time when the object was changed |
| When-Created | UTC time when the object was created |
By keeping track of the USN-Changed/USN-Created or When-Changed/When-Created attribute pairs, an application can identify changes that have occurred in the Microsoft Exchange Server directory since the last time it polled for changes. For more information on using these attributes to track changes, see Selecting Objects to Export and BatchExport.
By default, these attributes are available to authenticated users but not to anonymous users.