exchange tracking

Does anyone know why i would have a problem tracking messages in exchange? I can track external messages to an internal user. I can track all messages from an internal user. Yet when i try from one internal to another or by tracking number i come up blank. I have gone to microsofts sight and searched but all querries come up to be no help.
TIA

Are your internal users all on the same server? If you track internally via different servers, the MTA tracking option must be enabled on both servers.