Cannot send email to China

Need Help ASAP.

My company has reps and customers in China and other various countries. We have Exch 5.5 with latest service pack on NT4sp6a. We cannot get email to go through to only our rep and customers in China. They hang in the Outbound queue on the Exchange server with the details “Network error during host resolution”. Could this be a problem on our side or is it on the host side?

Thanks so much in advance!

Caron.