Microsoft Word includes a component that permits you to use Word to edit your e-mail messages in Microsoft Outlook. This step-by-step article describes how to configure Outlook to use Word to edit your e-mail messages.
Use Microsoft Word as Your Default E-Mail Editor
To turn Word on or off as your e-mail editor, follow these steps:
On the Tools menu, click Options, and then click the Mail Format tab.
Click to select or clear the Use Microsoft Word to edit e-mail messages check box, and then click OK.