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<sect1 id="server-usage-services">
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<title>Administering Internet Services</title>
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<para>
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The information generated inside the server computer is
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isolated from Internet. This way, any information generated
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inside the server computer will be available only to people
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registered inside the server computer. For example, don't ever
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expect to send/receive e-mails to/from Internet e-mail
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accounts like Gmail or Yahoo, nor visiting web sites like
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<ulink url="http://www.google.com/">Google</ulink> or
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url="http://www.wikipedia.org/">Wikipedia</ulink> either. For
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this to happen, it is required an established connection
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between the server computer you are establishing connection
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through and the Internet network those services are available
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in. Without that link, it is not possible to direct your
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requests to those sites.
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</para>
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<para>
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The implementation of services that required persistent
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connections (e.g., <application>chats</application>) will not
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be considered as a practical offer inside the server computer.
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Instead, only asynchronous services (e.g.,
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<application>e-mail</application>) will be supported. This
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restriction is required to reduce the amount of time demanded
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by services. For example, consider an environment where you
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connect to the server computer for sending/receiving e-mails
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messages and then quickly disconnect from it to free the
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telephone line for others to use. In this environment, there
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is no need for you and other person to be both connected at
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the same time to send/receive e-mail messages to/from each
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other. The e-mails sent from other person to you will be
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available in your mailbox the next time you get connected to
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the server computer and use your e-mail client to send/receive
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e-mail messages. Likewise, you don't need to be connected to
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the server computer in order to write your e-mail messages.
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You can write down your messages off-line and then establish
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connection once you've finished writing, just to send them
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out and receive new messages that could have been probably
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sent to you.
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</para>
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<para>
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Another issue related to e-mail exchange is the protocol used
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to receive messages. Presently, there are two popular ways to
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do this, one is through IMAP and another through POP3. When
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you use IMAP protocol, e-mail messages are retained in the
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server computer and aren't downloaded to client computer.
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Otherwise, when you use POP3 protocol, e-mail messages are
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downloaded to the client computer and removed from server
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computer. Based on the resources we have and the kind of link
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used by the client computer to connect the server computer,
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using POP3 is rather prefered than IMAP. However both are made
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available.
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</para>
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<para>
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Assuming you use IMAP protocol to read your mailbox, be aware
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that you need to be connected to the server computer. Once
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the connection is lost you won't be able to read your messages
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(unless your e-mail client possesses a feature that let you
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reading messages off-line). Morover, you run the risk of
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getting your mailbox out of space. If your mailbox gets out of
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space, new messages sent to you will not be deliver to your
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mailbox. Instead, they will be deferred for a period of time
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(e.g., about 5 days when using
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<application>Postfix</application> defaults) hoping you to
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free the space in your mailbox to deliver them. If you don't
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free space within this period of time, the deferred e-mails
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will be bounced back to their senders and you will never see
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them. On the other hand, assuming you are using POP3 protocol
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to read your mailbox, you always keep your mailbox free to
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receive new e-mails messages and keep them for you until the
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next time you establish connection with the server computer
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and download them to your client computer using your e-mail
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client.
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</para>
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</sect1>
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