You can view email messages in two formats.
HTML. HTML messages can have text formatting, numbering, bullets, colored background, and links which can make messages easier to read. Some email clients may not accept messages formatted in HTML.
Text. Plain text messages are messages that contain no HTML formatting code. Messages sent in plain text can always be read by other email clients. You can view messages in plain-text mode even if it contains HTML.
To always view your email messages in HTML, In Preferences>Mail select As HTML (when possible). Messages are displayed in formatted layout if they were sent in HTML.
See Also Setting your user preferences.