When running the Server Activity Reports some servers do not appear in the report.
Server Activity reports are populated by the Exchange Message Tracking log gathering tasks. If these tasks are failing or finding 0 eligable files the reports will not include data for these servers.
For complete statistical data it is important that MessageStats is able to gather message Tracking logs from every Exchange 2003 server, and every Exchange 2007 / 2010 Hub Transport and Edge server in the Exchange Organization.
If the Message Tracking Log folder is not shared using the default share name, this can be modified on the properties of each Exchange server in the MessageStats Console, using the "Tracking Logs" tab.