This article explains how to add rich text formatting to emails in the iPhone Mail app. Rich text formatting is available in iOS 5 and later.
Rich text to plain text in Apple Mail
Plain text emails don’t always convey what you want to say clearly. Like all forms of electronic communication, it lacks the nuance of face-to-face conversation. One way to add more expression to your iPhone emails is to use rich text.
To change the appearance of text in a message:
Open the Mail app on your iPhone.
