<sect1 id="server-usage-services">

    <title>Administering Internet Services</title>

    <para>
        The information generated inside the server computer is
        isolated from Internet. This way, any information generated
        inside the server computer will be available only to people
        registered inside the server computer. For example, don't ever
        expect to send/receive e-mails to/from Internet e-mail
        accounts like Gmail or Yahoo, nor visiting web sites like
        <ulink url="http://www.google.com/">Google</ulink> or <ulink
        url="http://www.wikipedia.org/">Wikipedia</ulink> either. For
        this to happen, it is required an established connection
        between the server computer you are establishing connection
        through and the Internet network those services are available
        in. Without that link, it is not possible to direct your
        requests to those sites.
    </para>

    <para>
        The implementation of services that required persistent
        connections (e.g., <application>chats</application>) will not
        be considered as a practical offer inside the server computer.
        Instead, only asynchronous services (e.g.,
        <application>e-mail</application>) will be supported. This
        restriction is required to reduce the amount of time demanded
        by services. For example, consider an environment where you
        connect to the server computer for sending/receiving e-mails
        messages and then quickly disconnect from it to free the
        telephone line for others to use.  In this environment, there
        is no need for you and other person to be both connected at
        the same time to send/receive e-mail messages to/from each
        other.  The e-mails sent from other person to you will be
        available in your mailbox the next time you get connected to
        the server computer and use your e-mail client to send/receive
        e-mail messages.  Likewise, you don't need to be connected to
        the server computer in order to write your e-mail messages.
        You can write down your messages off-line and then establish
        connection once you've finished writing, just to send them
        out and receive new messages that could have been probably
        sent to you.
    </para>

    <para>
        Another issue related to e-mail exchange is the protocol used
        to receive messages. Presently, there are two popular ways to
        do this, one is through IMAP and another through POP3.  When
        you use IMAP protocol, e-mail messages are retained in the
        server computer and aren't downloaded to client computer.
        Otherwise, when you use POP3 protocol, e-mail messages are
        downloaded to the client computer and removed from server
        computer. Based on the resources we have and the kind of link
        used by the client computer to connect the server computer,
        using POP3 is rather prefered than IMAP. However both are made
        available.
    </para>

    <para>
        Assuming you use IMAP protocol to read your mailbox, be aware
        that you need to be connected to the server computer.  Once
        the connection is lost you won't be able to read your messages
        (unless your e-mail client possesses a feature that let you
        reading messages off-line). Morover, you run the risk of
        getting your mailbox out of space. If your mailbox gets out of
        space, new messages sent to you will not be deliver to your
        mailbox.  Instead, they will be deferred for a period of time
        (e.g., about 5 days when using
        <application>Postfix</application> defaults) hoping you to
        free the space in your mailbox to deliver them.  If you don't
        free space within this period of time, the deferred e-mails
        will be bounced back to their senders and you will never see
        them.  On the other hand, assuming you are using POP3 protocol
        to read your mailbox, you always keep your mailbox free to
        receive new e-mails messages and keep them for you until the
        next time you establish connection with the server computer
        and download them to your client computer using your e-mail
        client.
    </para>

</sect1>