simpim, what server are u running?
In a single-server Exchange 2007 setup you'll need to allow annonymous connections on your default receive connector. By default Exchange 2007 servers not running the Edge Transport role will only accept inbound smtp connections from Exchange Users (clients), Exchange Servers (other Exchange 2007 servers) and Exchange Legacy Servers (legacy Exchange 2003 & below servers). To allow annonymous smtp connections for your server, run the following management shell command:
Set-ReceiveConnector -Identity "Default <ServerName>" -PermissionsGroup "AnonymousUsers"