Note that the "Destructing Message" service has an interesting twist: It doesn't identify the sender. Of course, you can identify yourself in the message, but you don't have to. It's both temporary and anonymous. Some email services, including Gmail, may block incoming mail from Destructing Message.
There's a related type of service that's useful when you want to keep a link private. You paste your link into the service, and set the "expiration date." Then, the service creates a temporary link that leads to the real link.
Note that Dying Links is highly configurable, enabling you to specify a delayed activation, an expiration date and time, and even a maximum number of clicks before it expires. It also shortens URLs.
Sometimes you just want to show someone a picture, but you want to do it securely and privately. In that case, you might try SnapChat.
SnapChat is an iOS and Android app that lets you send pictures from your phone to a list of recipients, who can view the picture only from within the SnapChat application, and only for a maximum of 10 seconds. The sender can even choose to set the time limit to less than 10 seconds.
While the picture is displayed, the screen capture feature on the recipient's phone is disabled.
Are these services unethical?
Some of you might think that these services are unethical and are only for people with shameful secrets to hide.
But I'm not here to lecture you about your ethics. That's your business, not mine.
I'm here to lecture you about being smart when using email, social networks and other online communications media. Whether you use these services or not, you should know they exist, just in case.
Learn from Petraeus's bad example: Start exercising common sense and avoiding the traps of myopic thinking and "present bias." And start taking advantage of some of the free and easy apps that can keep your secrets secret. With these tools, you can enjoy the benefits of online communication without the risks.
You're a smart person (if you're reading my column, you MUST be smart). So don't do something dumb like Petraeus did. Be smart -- and communicate smart.