With the launch of Windows Live Hotmail, Microsoft has announced Windows Live Mail, the desktop client that is reportedly meant to succeed Outlook Express and Vista's Windows Mail by replacing Windows Live Mail desktop, currently in beta. The first beta build of Windows Live Mail, available in a few short weeks, is supposed to incorporate features of all three of the aforementioned applications.
With the name change there are a few features that will be added to the current WLMd software. First off, an improved user interface with Aero support will give you control of your e-mail, without any graphical advertisements. Note that the loophole for textual ads was left wide open. Setup and account migration improvements should cut down the steps to get started with the client. Taking from OE and WM, S/MIME and LDAP support will be added to WLM. The new client is also being touted as faster and more robust than WLMd. As before, Windows XP SP2 and Windows Vista will be the two supported operating systems.
News source: Windows Live Mail Blog