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DEFINITION:

Self-destructing email is electronic mail that vanishes or becomes unreadable after a certain length of time or upon the request of the sender. Although self-destructing email technologies has existed for years, none has been very effective. Several new programs are said to offer better performance as well as email security and privacy enhancements.

There are two main types of self-destructing  … 
Definition continues below.

EMAIL SECURITY SERVICES DEFINITION (continued): …  email. The first type, also known as retractable email, allows the sender to cancel or void a transmitted message as long as it has not yet been read by the intended recipient. The second type of self-destructing email theoretically disappears from the Internet altogether after a certain length of time has passed. The key word here is "theoretically" because if the recipient sees an email message preservation is always possible -- even if it means taking a photograph of the display screen on which the message appears or having multiple witnesses view the display in real … 
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