Mailbox unavailable. The server response was: 5.7.1

Hello,

 I want to send a mail since a page aspx, that works over windows 2003 server. The smtp service is configurated:

IIS > Default SMTP Server > Properties > Access > Authentication

Access Control > Anonymous access - Checked
Relay restrictions > Relay > - Only the list below (add the LAN IP address of the web server)

but when i send, the message appears:

Mailbox unavailable. The server response was: 5.7.1 Unable to relay for test@domain.com.

The code is:
MailMessage correo = new MailMessage();correo.From = new< ...