I believe you can use the Stationery to change default fonts options. In Outlook 2007 locate your options menu..Should be File options or tools . Options..Then Select mail options and "use Stationery to change default fonts and styles,colors and backgrounds".



Within the "Personal Stationery tab, under "Composing and reading plain text messages select the Font button. Customize at will.

Hope this helps.

Stationery only has options for the mail that you create and reading plain text messages (which are not the kind of messages that worry me). Any other ideas?