I’ve had a number of customers asking how they can block certain devices from connecting to Exchange.  This has arisen primarily around many IT departments being uncomfortable with people using an iPhone to connect to their corporate Exchange environment due to security concerns over the iPhone platform.

Now if you are using ISA as your firewall then you can block an iPhone (or other devices by inspecting the HTTP header)

To do this right click on the Activesync rule, choose Configure HTTP and then do the following

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