smtp error code

When one of our users sends to a certain email address, this is the bounce back that she gets- #5.5.0 smtp;553 sorry, that domain isn’t in my list of allowed rcpthosts (#5.7.1)>
In the past, when we’ve seen this error, there has been a configuration error on the remote server. We run an Exchange 2000 server. I just want to verify that this is not an Exchange error message. Everything I find about this error message points to a qmail server. Is this right?