web.config mailSettings

I am getting this error when sending mail from both my local host and web server:

Syntax error in parameters or arguments. The server response was: 5.7.1 <support@xxx.net>... Permission Denied
On the client.send:
                    Dim client As New SmtpClient()
                    client.Send(message)

the from and to addresses are valid.

This is what I have in my web.config:

    <system.net>
        <mailSettings>
            <smtp deliveryMethod="Network" from="support@xxx.net">
                <network host="mail.xxx.net" port="25" userName="xxx" password="xxx"/>
            </smtp>
        </mailSettings>
    </system.net>

I have also tried the host as the actual IP address for the mail server too.

I do have a firewall. the mail server is setup in the firewall and is very actively in use, but from another web server with asp classic pages.

I have a netgear firewall.
So there are 3 servers, web server 2000 which sends mail fine, web server2008 which is new and hasn't yet sent mail, and mail server.

What am I lacking?

I don't know what deliveryMethod I should use. Saw it in an example.

thanks.