Can’t Send Email to Certain Domain

Running Exchange 2k3 on a W2k3 server.

I am having problems sending email to certain domain. Receiving emails from them is no problem. I only have problem sending to them.

I enabled the Logging on my SMTP Virtual Server. There is one thing in command on all these domain I can’t email to. They all gave me an error of “command line too long.” One error message said ” 421 5.5.2 Syntax error (command line too long).” Another one said ” 500 Command line too long.”

Please help!