Any message you have ever sent to anyone since your first account lives on.
Chances are it remains on the recipient's hard drive.
Otherwise, it could linger on the server that either sent or received the original message. And if either the sender or the recipient used a corporate e-mail account, the message is probably backed up in two or three places. In this respect, e-mail isn't any different from any modern form of communication. You may have a conversation in a public place, on the street or in a restaurant, and someone can catch the whole thing with a long-range microphone. With all the available technology, it's possible that everything we say and do is monitored in some way.