Invalid Sender

[Lack]

Has anyone ever had this in Exchange 2003?
-There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <server.DOMAIN #5.5.0 smtp;553 Invalid sender: username@domain.com>-

Of course, the email and domain part have been changed to generic. Any help would be appreciated.

 

[Lack]

Has anyone ever heard of this? Please see below..

 

[Lack]

Has anyone ever had this in Exchange 2003?

I am trying to send an email to a company in China. The domain name is legit but I keep getting this bounce back. They had actually sent an email to me telling me to "add their email address in our SMTP system in OUTLOOK EXPRESS, otherwise, our email to them will be filtered out as "trash" email and returned to sender." We are using Outlook 2003 with Exchange Server 2003. Any ideas? Here's the error:

-There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <server.DOMAIN #5.5.0 smtp;553 Invalid sender: username@domain.com>-

Of course, the email and domain part have been changed to generic. Any help would be appreciated.