Disappearing Email is developed by Disappearing, which already offers a version for corporations. That product lets system managers set e-mail policies and includes several sophisticated features.
The free edition for Outlook, which becomes available this week, focuses on simplicity. When you download the Disappearing Email for Microsoft Outlook plug-in (about 350KB) from Disappearing's Web site, it's automatically installed and a "Send Disappearing" icon appears on the Outlook toolbar. (The plug-in doesn't currently work with Outlook Express.)
This entire product is a gimmick, based on naive assumptions and a lack of technical understanding. Requiring Microsoft Outlook (and not Express) is the first warning flag for potential customers. It warns us that e-mail recipients that don't use Outlook may not be subject to the 'rules' put in place by the software.
But after the time limit specified by the sender, the decryption key is erased from Disappearing's key server, making the message unreadable and effectively destroying it, even if the recipient stored it.
This is patently false. If I receive an e-mail "protected" by this scheme, there are a number of ways I can store the mail so as not to be affected by Disappearing's attempt to delete it. I can cut/paste the text of the mail into a file or I can forward the decrypted message to another e-mail address. If such a "protected" message is sent to a person that uses something other than Outlook, the message can be kept in their inbox safely.
The free version of Disappearing Email doesn't offer some of the more sophisticated features of the corporate version. The free version can't call back a message before it's read, or track when messages have been read.
Again, the only way to determine if a message has been read by a remote recipient is if they run a client that answers such requests (e.g., Outlook, and not the default behavior), or they load remote content (e.g., a "web bug") that lets the remote server know it was opened. The notion of "calling back a message before it's read" is Outlook specific, and not supported by almost any other e-mail client.