There are three modes available for the Webmail interface, each of them have some differences in features and layout.
The Dynamic mode has more of an Outlook feel and flow to it. It features a preview pane and allows dragging and dropping of one or more emails. This mode is selected by default the first time you login.
The Traditional mode has more of a standard Webmail look and feel to it. It also features an enhanced portal view that allows for additional customization; for instance you can add the current time or local weather.
The Minimalist mode is very basic and is intended for use with basic Mobile web browsers.
You can login with any mode by simply selecting it in the drop down menu on the login screen.