Recently I shared a service called SelfDestructing, PrivNote is another similar service which lets you send private notes to your friend that self destruct after reading it once.After you create your note you get a link that you can share with you friend.Once the user closes the window the message is no longer available for reading.All notes are stored encrypted on the servers, before they are self destroyed or not read before 30 days.

There is also a provision for getting a confirmation when your private message was read, to the email id you can provide while creating the private note.