Exchange Server 2000 error

From a couple of sites I get this error and cannot figure out why? For all other sites we have no probelms. .4.7 I left the message below. Aaron

Delivery Failure Report
Your Expedite Request for Part Number CI222-1
document:
was not TDruke@comant.com delivered
to
: because: Enhanced Mail System Status Code (RFC1893): .4.7
"Theresa Druke" on 06/06/2002 03:19:48 PM

Please respond to "Theresa Druke"

To: "Margie Edwards"
cc:

Subject: test