(With the development of the Internet, e-mail has gradually spread as a communication method. At that time, the users of e-mail have developed from the science/academic and educational industries to the users in ordinary households, and the information transmitted by e-mail has also developed from general text information to multimedia information including sound and images. The cheapness and simple operation of e-mail not only bring infinite convenience to everyone, but also induce some people to use it as a tool to send a large number of their own information, which eventually leads to the proliferation of spam in the Internet world.
11-Using Layer Security.ppt)
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