When viewing the Diagnostics Console in Spotlight on Exchange you see a warning status for Best Practices: One or more SMTP Virtual Servers could be used for relaying mail.
Spotlight on Exchange gets this information from the RelayForAuth property in the IIS Metabase. If RelayForAuth is Set to 1 then it means that the
Allow all computers which successfully authenticate to relay, regardless of the list above check box is checked for the SMTP Virtual Server.
The default Exchange 2000/2003 configuration does not allow unauthenticated users to relay through the server. Please check the status of the Allow all computers which successfully authenticate to relay, regardless of the list above check box and configure accordingly.
For more information about Mail Relaying and Exchange 2000/2003 please refer to the following:
http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/58f05ef9-55a3-42b3-9f57-27fdc8723b8a.mspx?mfr=true
http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/eb361c8a-91fd-4e5c-803e-3681887ddc40.mspx?mfr=true
