Ok this question is kind of two parted.
We have just purchased a barracuda antispam 300 device that is working fairly well. I have fiddled with our DNS server entries and pointed all MX records away from our exchange server and pointed them directly into the barracuda (Although their are still DNS entries pointing to our Exchange server for other reasons.) Mail is somehow bypassing my barracuda and going directly to the exchange server. This is causing the server to receive spam that goes directly to users inboxes without the barracuda filtering it. I assume that the spammers are spamming my DNS entry of jblanchard@mail.%domainname%.com instead of jblanchard@%domainname%.com and this is causing the problem.
1.) Can I block incoming smtp port 25 to my exchange server without interupting the flow of outgoing email? I.E. if I block port 25 on my firewall to the exchange server will other servers be able to successfully communicate with my exchange server when It needs to transmit email messages?
2.) is there settings in exchange 2003 that will allow me only to receive email from a list of IP addresses I specifiy? IE I provide exchange the IP address of my barracuda and make it so that it will only accept messages from the barracuda?
1.) is there settings in exchange 2003 that I could