Expiring email, deletable email, certified read receipts - ReadNotify has it all. And they have several worthy competitors. Google them up for yourself.

In 2003 I implemented it across a law firm - 18 months later the principal rang all excited explaining that he had just used the receipts in the Supreme Court to prove that not only did the other party receive the email but it had also been read by a number of other people in the company as well as their legal advisors. From further analysis they were able to determine the exact times of telephone discussions of the email between the recipient & his lawyer.

The firm always uses ReadNotifys deletable / expiring email to send sensitive data.

We also have another support customer who have implemented ReadNotify across their sales department. They use it to determine when the recipient is opening/re-opening their quotes. Their sales people make 'timely' follow up calls a couple of hours later.

Other law firms, banks & anyone who deals with sensitive data would do well to investigate.