help major problem

From: concern (
Date: 01/11/03

From: "concern" <>
Date: Sat, 11 Jan 2003 10:51:31 -0800

I have a sql server that is using IIS to send email to
users in our domain. I am getting the following message
when IIS smtp service tried to send email from a user on
our exchange server to a user on our exchange server.

Message delivery to the remote domain '' failed.
The error message is 'An SMTP protocol error occurred.
'. The SMTP verb which caused the error is 'RCPT'. The
response from the remote server is '550 5.7.1 Unable to
relay for

has anyone seen this before. Also, this user can send
email to addresses outside of my domain with no problems.

I am using exchange 5.5 with service pack 4.