Message undeliverable

On our Exchange 5.5 server that runs a small company we receive the following message when sending emails to some companies not all.

“Your message did not reach some or all of the intended recipients.

Subject: Test message from XYX Company
Sent: 7/17/2002 2:29 PM

The following recipient(s) could not be reached:

‘c.rosillo@XYZcompany.com’ on 7/17/2002 2:29 PM
The recipient name is not recognized
The MTS-ID of the original message is: c=US;a= ;p=XYZCOMPANY.c;l=XYZCOMPANY-020717182842Z-12”

Any suggestions would be greatly appreciated.
Thanks in advance,
Mark