"James M." wrote:

> I keep receiving the following error message on my Win2003 IIS 6.0 SMTP
> server, when trying to relay mail to an Exchange 2003 server on my network.
> This error only appears when trying to send to the specific domain hosted on
> the Exchange server, and does not appear when sending mail to other domains.
> I am sending from the address DO_NOT_REPLY@<domain.com>, which an account
> does not exist for, but again, it works fine for other domains. Any ideas?
>
> --------------- Begin error message from System Event Log -----------------
> Message delivery to the host '<exchange 2003 server IP>' failed while
> delivering to the remote domain '<domain.com>' for the following reason: An
> SMTP protocol error occurred.
> The SMTP verb which caused the error is 'MAIL'. The response from the
> remote server is '553 Terminating connection as the sender is spoofed.
> '.