I have a Barracuda 300 spam firewall which is behind our router along with our SBS Exchange server. The MX record points to the external IP address of the router, port 25 is redirected to the Barracuda which is set to inbound monitoring of our SBS Exchange server. I have a bunch of iPhones whose provided Exchange server option is set to the MX entry and points to the router but is now redirected to the Barracuda rather than the SBS Exchange server.
Obviously, the iPhones aren't playing ball with the Barracuda. How do I get around this?