Error sending mail: Unable to relay (SMTP / IIS)

When trying to send mail from a website on my Windows 2003 server I get this error message:
The server rejected one or more recipient addresses. The server response was: 550 5.7.1 Unable to relay for (valid email).

After some searching I understand that nothing is wrong, but you are not allowed to relay (send the email). By default, the SMTP server in windows Server 2003 will not allow anyone
to relay. So you have to allow the local server to relay.

The solution should be this: Open IIS Manager, and right click the virtual server (ie "Default SMTP Virtual Server") and click Properties. Click on the Access tab, and click
the Relay button. Add the IP of the webserver to the list of machines
allowed to relay. This setting will allow your webserver to relay thru the SMTP server.

My problem is that there is no Default SMTP Virtual Server when I open IIS Manager. The SMTP Service is installed, if I open Add/Remove Windows Components - Application Server - IIS - SMTP Service it is checked. How can I allow to relay?? PS: This is Small Business Server 2003 R2, dont know if Exchange Server can be a issue? I dont use it... I think..?
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The smtp virtual server is in Exchange management Console
This picture will give show you exactly where it will be. The virtual SMTP server is in the Exchange management Console

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webressursAuthor Commented:
Ok, where do I find that? I cant see it in "Administrative tools" or "Control Panel". Do I have to use the Server Management tool? Thanks for helping me!!
Start-->Programs -->Microsoft Exchange -->System manager
Let me know if you require any more information ill guide you through
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