Open the Tools menu and choose Options.
The Options dialog box opens. Click the Mail Format tab.
To select a default format for new mail messages, click the down arrow next to the Compose in This Message Format field and select the format you want to use.
If you find that you constantly compose messages using Microsoft Word or some other message format, such as plain text, that is not Outlook's default setting, you can configure Outlook to use your preferred format by default.
To use Word to edit or read messages, check the Use Microsoft Word to Edit E-mail Messages and Use Microsoft Word to Read Rich Text E-mail Messages check boxes.
Changing the Default Font
To change the default font for new messages, replies, or forwarded messages, click the Fonts button in the Mail Format tab of the Options dialog box. Then, click the Choose Font button next to the message type whose font you want to change. Select the font, size, and style you want to use, and click OK once to close the Font dialog box, again to close the Fonts dialog box, and a third time to close the Options dialog box.