An external user is unable to connect to the Exchange 2007 RPC/HTTP Web site. But internal users are able to. Clearly, the problem is with the ISA firewall, right? WRONG. Remember, in over 99% of cases when the ISA firewall is correctly configured, it's not the firewall's fault -- it's something else causing the problem.
Check out this article by Yuri Diogenes that explicates the problem with the Exchange CAS that caused a situation that made it look like an ISA firewall issue.
Thomas W Shinder, M.D., MCSE
Sr. Consultant / Technical Writer