When I was looking for some privacy tools, I found one site for E-mail privacy. Its name is Stealth Message:
On this site you can create account and use with it, but it is not required...
First when you click on try it now, it will appear one form for sending the stealth message.
The features of this service are:
The self-destructing option;
128 Bit key encryption;
Highest anti-copying security;
Tracking recipient's address.
This can be used for very secret informations.
This methods also are used by FBI.
Actually I found this site on one FBI's sponsor website...