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March 05, 2005

I wish to correct one part of the technical description about how email works in Chapter 4. The first paragraph of page 37 incorrectly states that your email program downloads mail from the server in one swoop. While it may appear to be the case to the user, in truth, the most common email system described in this section (POP) transfers email messages to the email software on your PC one at a time, as the result of a "conversation" between your PC and the POP server. After the server authenticates your email program's connection request as being legit (e.g., through password verification), the typical "conversation" goes like this (translated into English):

• Your Email Software (Client): Got any mail for me?
• Server Software (Server): Yes, 2 messages.
• Client: Send me the first message.
• Server: OK. Here's how big it is, and here comes the message (followed by entire message content and an end marker).
• Client: Delete the first message on the server.
• Server: First message is marked for deletion.
• Client: Send me the second message.
• Server: OK. Here's how big it is, and here comes the message (followed by entire message content and an end marker).
• Client: Delete the second message on the server.
• Server: Second message is marked for deleteion.
• Client: I'm done. See ya!
• Server: Over and out.

With the successful close of the transaction between client and server, the server deletes from its email file those messages marked for deletion. The system is designed to prevent deletion of email on the server in the event of disruption during transfer of individual messages.