How to specify e-mail format in Microsoft Office Outlook 2007?
Global Change
Follow these steps to turn off TNEF:
  1. On the Tools menu, click Options.
  2. Click the Mail Format tab.
  3. In the Compose in this message format box, click Plain Text or HTML, and then click OK.
Follow these steps to send in TNEF:
  1. On the Tools menu, click Options, and then click the Mail Format tab.
  2. In the Compose in this message format box, click Rich Text, and then click OK.

How to specify e-mail format in Microsoft Office Outlook 2003 and earlier versions of Outlook

Global Change
Follow these steps to turn off TNEF:
  1. On the Tools menu, click Options, and then click the Mail Format tab.
  2. In the Send in this message format box, click Plain Text or HTML, and then click OK.
Follow these steps to send in TNEF:
  1. On the Tools menu, click Options, and then click the Mail Format tab.
  2. In the Send in this message format box, click to select Microsoft Outlook Rich Text Format, and then click OK.
Per Recipient Change
In the Contacts Folder
Follow these steps to turn off TNEF:
  1. Open the recipient's record in the Contacts folder.
  2. Double-click the recipient's e-mail address.
  3. Choose Send Plain Text only in the Internet Format box.
Follow these steps to send in TNEF:
  1. Open the recipient's record in the Contacts folder.
  2. Double-click the recipient's e-mail address.
  3. Click Send Using Outlook Rich Text Format in the Internet Format box.
In the Personal Address Book
Note Personal Address Books (.pab) can no longer be created or used in Outlook 2007.
Use the following steps to turn off TNEF:
  1. Locate the recipient in the Personal Address Book.
  2. Double-click the recipient's e-mail address.
  3. Click to clear the Always send to this recipient in Microsoft Exchange Rich Text Format check box, and then click OK.
Use the following steps to send in TNEF:
  1. Locate the recipient in the Personal Address Book.
  2. Double-click the recipient's e-mail address.
  3. Click to select the Always send to this recipient in Microsoft Exchange Rich Text Format check box, and then click OK.
Per message change in Outlook 2007
Use the following steps to turn off TNEF:
  1. Open a new mail message, or click Reply on a received message.
  2. On the Options tab, click HTML or Plain Text.
Use the following steps to turn on TNEF:
  1. Open a new mail message, or click Reply on a received message.
  2. On the Options tab, click Rich Text.
Per message change in Outlook 2003 and earlier versions of Outlook
Use the following steps to turn off TNEF.
  1. Open a New mail message, or click Reply on a recently received message.
  2. On the Mail Format toolbar, click to select Plain Text or HTML from the dropdown menu.
Use the following steps to turn on TNEF.
  1. Open a New mail message, or click Reply on a recently received message.
  2. On the Mail Format toolbar, click to select Rich Text from the dropdown menu.