We run w2k3SBS with exchange, and we have a firebox x500. We have an SMTP proxy because we use NAT to take incoming mail to our external IP and fwd them to our internal server IP. Outgoing smtp is from our internal server IP to Any.
Our outside sales guy lives by his usa.net email and so we just fwd his company email to his usa.net account (smtp.postoffice.net). When he is in the building he can surf around and do most things, but he can not send email via port 25.
He can log in and use webmail to send, but he can not send via Outlook.
My guess is this: because the smtp proxy wants to see SMTP traffic coming from the server's IP, and because Mr. Salesman's laptop has a different IP, the firewall blocks it. I have tried adding a host IP, host name, network IP, etc. The firebox sees his computer, but still, he can not send smtp traffic out.
Last week we had a DNS issue where we ended up deleting the DNS proxy and recreated a DNS Filter instead. It seems this would be the thing to do here for the SMTP issue, however we use NAT, and I couldn't see that the SMTP Filter would allow me to recreate a similar NAT. Any thoughts?