How do I Allow Exchange 5.5 to accept connections

[Adminman]

How do I Allow Exchange 5.5 to only accept SMTP connections from one source? We are using Postini spam filtering and the spammers are sending e-mail directly to exchange's IP address. I have the ip range to add, but I'm not sure where to add it. I was thinking IMS... not sure. Server does see connections from postini via event ID 2000.

Network structure

one exchange 5.5 server running on NT4.
Flowpoint router running NAT
Sonicwall 230pro firewall

Thanks,

Adminman

 

[Atch007]

In Exchange Administrator, go to 'Connections', then open properties on your Internet Mail Connector.
On the Connections tab, check Accept Connections Only From Hosts using: Authentication. Then click 'Specify by Host...' and add the IP address of the SPAM filter server that is allowed to relay messages to your Exchange box.
That will close off any open relaying.

Brad