ASKER
Hardware-based firewalls provide more sophisticated protection for inbound and outbound traffic than the simple Windows software firewall or the basic NAT firewalls found in routers. These devices implement techniques such as stateful packet inspection, deep packet inspection, and content filtering; and may include built-in antivirus and anti-malware protection.
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Open your isa server management console , right click on firewall policy select new/non web server protocol publishing rule... on first screen give a name , second screen type ip address of your exchange server , on next screen (select protocol) click on new , give a name to protocol (ex. spamfighter) , on next screen click on new again , select protocol type as udp , do not change direction , type port range both on from and to as 2409.Click on next 2 times and click finish.On main screen click next again. Select external on network listener IP Address window then click next and finish. You shoud also click on apply button to activate the rule.