I have a W2K LAN with an Exchange Server 2000 and and ISA Server 2000. Everything was working OK. I then decided to upgrade all of my workstations (& exchange server) to Firewall Clients. Downloaded the white paper from isaserver.org. Did as instructed. Everything SEEMED to be OK and working perfectly. Shortly afterwards, I was not able to send emails. I could receive, but not send. (Though I could reply). I could surf the Internet OK. No problems! Shortly after that, I found out that I could only send emails to addresses that weren't re-routed to another email address. (This appeared to be why 'Reply' worked as it always sends the email to the final destination directly). I disabled all of the firewall client connections and reverted back to web access clients. (My original configuration - which worked). That didn't help! I checked everything I could think of. Nothing had changed from my original "working" configuration. I GIVE UP! Can anyone offer any clues as to what is going on?