The current message, if any, is displayed in the bottom subwindow. The uninteresting mail header fields are initially scrolled off the top of this display. You can control which fields are displayed with the Header-Display: and Header-Suppress: profile entries as described in the Section MH Profile. The Section Colorizing Header Fields describes how to colorize different header fields.
Pressing the space bar pages through the message -- or takes you to the next message if you are at the end of the current message. Backspace brings you back a page. You can also scroll the message with the mouse by using the scrollbar or by drag-scrolling with the second mouse button.
exmh displays a watch cursor in the message window while it computes the display of a MIME message. On a color display, a MIME message body is displayed in a slightly darker background. This shading is used to indicate the depth of nesting in a multipart MIME structure.
A popup menu controls MIME message processing such as saving contents or rendering contents with an external viewer. Press the third mouse button in the message display area to obtain this menu. Make sure you press the mouse button over the message body, not the header. For multipart messages, the menu changes depending on the part of the message you're viewing. See also the Preferences entry for MIME for some parameters you can adjust.
You can display a message in a new top-level window. This lets you keep the message anywhere on your display. Use the Clip operation under the message More... menu. It displays the current message in a new, larger window.