Unread mail count on iPhone / iPad is often out of date
Unfortunately No

As far as Apple is concerned this is by design, and even the latest mail upgrade on MobileMe did not enable this functionality. This has been discussed at length on the Apple forums and hopefully at some point this change will be made.

There is no known workaround, as this is controlled by the server, and not the local app. Even jailbroken their is no solution I am aware of.