Are you trying to read characters in a non-US-language email? If so, you can change Yahoo! Mail’s character encoding setting. It’s easy! Here’s how:

1. At the very bottom of the message, under the message window, look in the lower-right corner, where you'll see a down-arrow next to a pull-down menu with the words, "Select Message Encoding".
2. Click the down-arrow, and from the list that appears, select the encoding that matches the message’s content.

Note: In this case, changing your browser’s encoding setting will not work.