If you want to keep your email conversations “off the record”, you might want to consider sending an email that fades away as soon as it’s opened. You can do this by using a simple browser extension like “Fade.li” for Chrome.
You don't even need the browser extension to use the service.
Just add add .fade.li at the end of a mail and it works.
I'd not heard of such a service, although it seems that there are a few more out there but others might not be aware.
I originally found about it from dotTech, so kudos has to go to them.http://dottech.org/160468/chrome-fade-li-review/
The only limitations seems to be that you are restricted to 50 mails a day, which makes sense.http://fade.li/