"This Email Will Self Destruct" (opens in new tab)

There are several techniques, some of them are:

* Show in a frame on the company's server

* Sends JavaScript code that retrieves the message from the server

* Sends an ActiveX / Java / Flash client that displays the message from the server and resists attempts to copy/paste

* Sends the file with DRM, and a client that would enforce the DRM rules

Being that the website uses flash on its first page, I would hazard a guess that a Flash client is involved. I don't like to login to these sites with credentials from other sites, especially if I only want a bit of information.

By the way the idea isn't new by any stretch of the word. http://readnotify.com have been at it for years.

[edited for formatting]

Or an iframe, or javascript that retrieves data from a server. Fun idea, but more trouble than it's worth, given how mail clients could bork a complicated implementation.