I am not an Exchange server engineer, but I have a related problem that needs to be pointed out to Microsoft.I am a contract programmer running Microsoft Windows Vista Business with Microsoft IE 7. I have an email account at one of my client companies. The vast majority of the company's computers are running XP Pro. The email was recently moved to Microsoft Exchange Server (2003?). The email clients are Microsoft Outlook Web Access.I could not reply to or create a new message with IE7. (I could with Firefox). After some asking around and Googling, I found that I needed to install S/MIME control. I did that, and could then reply to a message. Once. IE 7 then crashed. I reboot, re-install S/MIME, try to pay attention to all the yellow bars, etc. -- no luck. More Googling. AHA! There is a "hotfix" to be applied to the Exchange Server. I discussed this with the network engineer who told me that it was a Vista thing (Other IE7 users on XP were not having a problem) and that he would not support Vista. (I don't blame him.) He suggested using regular Outlook 2003 which I tried, but I decided that I would rather use the web client in Firefox. (For one thing I am already using Outlook for my main email account, and switching is a pain.)So in a nutshell, Microsoft's "latest and greatest" operating system and established Microsoft Exchange Server and Outlook products do not play nice together. I would also like to point out that this problem will affect home users as they buy new Vista machines. Most of these people could not, and should not have to, troubleshoot this problem.The solution is to use Firefox. Go figure.

http://support.microsoft.com/kb/911829 I think, your client uses illegal copy of Exchange 2000, and that is the reason the network engineer refuses to make a contact to Microsoft Customer Support Services to obtain the hotfix