Rich text formatting is available in iOS 5 and up.
Like all forms of electronic communication, it lacks the nuance of face-to-face conversation.
One way to add more expression to your iPhone mail messages is to use rich text.

To change the look of text in a message:
Open theMailapp on your iPhone.
Tap thenew emailicon at the bottom of the screen to open a New Message screen.
Enter the recipient, subject, and message as you usually do.

opt for text that you want to apply rich text formatting to.
Either double-tap a word or tap and drag the text handles to expand your selection.
Tap the arrow at the right side of the toolbar that appears above the selection to see additional options.

TapBIUto expand it to show the Bold, Italic, and Underline options.
Tap the option you want to use on the selected text.
Tap any blank area of the email to save the formatting and kill the formatting bar.
Repeat the process for any additional formatting you want to make in the email.
What’s Rich Text?
Rich text messages are a step between plain text and HTML.
Some email programs don’t supportHTML emails, so using rich text offers a compromise.
Plus, it’s straightforward to use on amobile devicesuch as the iPhone.