MS Exchange Server 5.5

I’ve loaded MS Exchange Server 5.5 on Win2K. I’m having a problem sending email out. Recieving email I don’t have a problem.

This is the error message: The recipient is not recognized:
the MTS-ID of the original message is : c=us;a=;p=exchangep;l=exchangep-000913184535z-1
M:msexchangeMTA:excsexchangep;exchangep