Update 19/02/06 - The tool that can be downloaded from here has resolved the domain traversal issue. The install bug with the default web IP needing to be reset to "all unassigned" remains.
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The Exchange Server ActiveSync Web Administration Tool was released on the 7/12/05, to enable remote wipe of AKU2.0 (windows mobile 5 devices with the MSFP) phones and Pocket Pc's.
If you read the release notes on the download page, you will see the statement:
"To function properly, the tool must be used in conjunction with Exchange Server 2003 Service Pack 2 and compatible mobile devices.
The current release of the Exchange ActiveSync Web Administration Tool must be installed in the same domain as the user accounts being managed."
To further explain this, if you are an enterprise who puts mailboxes into a resource domain, and accounts in another resource domain, the tool cannot resolve the user accounts. The tool will only install on an exchange server, and placement of the tool in user accounts domain will still not solve the problem.
The tool itself is a quick and easy install, which creates a virtual directory in IIS called MobileAdmin. An additional bug sometimes occurs if your default web site is set to use a specific IP address rather than "all unassigned". It will create an additional "default web site" instance. To remedy this, set the IP address of the default web site to "all unassigned", then change back when finished the install.
An updated version of the Mobile admin tool (06.05.7775) was released on the 2/01/06, which also has the same issues.
Microsoft has a fix, but you will need to contact them to get it for the moment.