It depends of how you display the message. Generally speaking, you can send HTML mail messages, which allow you to format text as you want.

Anyway you can't be sure that the mail client used to read the message supports HTML mail, so you have to create a Multipart/alternative message to embed the parts of the message: the first part is text/plain and the other part is text/html, with formatted text.

The way this multipart is handled by the client is none of your business: one client could show the HTML part, one other could show the text part.