Use the Tools, Options, Other, Preview Pane (or Reading Pane when using Outlook 2003) dialog to change how messages are marked as read.
You can also access the preview pane options changes by right clicking on the preview pane header in earlier versions of Outlook or on the gray border of the reading pane in Outlook 2003. In Outlook 2003, you can change the location of the reading pane or change the font size used on HTML messages from this dialog.
Change the font size for plain text messages from Tools, Options, Mail Format tab, Fonts button, by changing the plain text font option.
Published September 15, 2003. Last updated on May 16, 2011.