Mailing list messages that might offend some readers are sometimes encoded in a simple code called rot13--so named because it rotates the alphabet by 13 letters. This code is not for secrecy, as it provides none; rather, it enables those who might be offended to avoid ever seeing the real text of the message.
To view a buffer using the rot13 code, use the command M-x rot13-other-window. This displays the current buffer in another window which applies the code when displaying the text.