I can't change the formatting of a message when replying or forwarding
When replying to or forwarding an e-mail message, you are unable to format text or insert a picture in the message body.
Of the three message formats that Microsoft Outlook supports — plain text, Rich Text Format (RTF), and HTML — plain text does not support inserting a picture or formatting text, such as adding bold fonts, colored fonts, and bullets.
When you reply to or forward a message, Outlook preserves the format of the original message. Also, if you select the Read all standard mail in plain text option, Outlook formats your reply in plain text.
If you are replying to or forwarding an e-mail message that was sent in plain text format, you can change the message format to HTML. This enables you to insert pictures or add formatting to the text.
Change message format
To change the format of the message when you reply to or forward a message, do the following:
Click Reply, Reply All, or Forward.
In the message window, on the Options tab, in the Format group, click HTML.