Self Destructing emails delete the original message once it has been read by the recipient.
Here are a few self destructing email providers that you might find useful for sending emails.
WillSelfDestruct: This site enables you to create a one-time secure web page for a recipient. You can create a secure anonymous email message to a friend or colleague by entering their e-mail address and the message. The recipient will receive an e-mail with a link to a one-time secure web page which they will be able to view once and only once. Once the url has been accessed the message is deleted.
StealthMessage: Stealth Message allows encryption of email mesages, stores encrypted messsages anonymously, set self-destructing options, prevent forwarding and copying of messages
ZMail Basic: Allows you to specify a Release Time wherein a message cannot be read before the time you define, Expiration Time wherein an email cannot be read after the time you define and Delivery reciept which shows When, Where, How and by Whom your message was decrypted
There are more here.
