When you attach a file to an email message, the message format determines how the attachment appears in the Outlook message window.
Plain text or HTML format messages
Rich Text Format (RTF) messages
When you reply to a message, by default, the format of the received message is used for your reply. To change the message format when composing a message, do the following:
- On the Format Text tab, in the Format group, click HTML, Plain Text, or Rich Text.