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<sect1 id="configurations-dialup-usage">
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<title>Usage Convenctions</title>
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<para>
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The infrastructure described in this chapter uses the
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client/server model to provide a public mail service through
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the telephone line. In this configuration, we (the poeple
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building the infrastructure) provide the information you (the
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person using the infrastructure) need to know in order to
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establish a point-to-point connection from your client
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computer to the server computer through the telephone line.
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</para>
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<para>
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The infrastructure described in this chapter is made available
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to you free of charge, however, you should know that
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maintaining it costs both money and time. For example, for
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each hour the server computer is on production there is an
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electrical consume that need to be paid every month.
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Likewise, each call that you establish from your client
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computer to the server computer will cost you money, based on
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the location you made the call from and the time you spend
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connected.
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</para>
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<para>
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In this section we discuss usage convenctions we all must be
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agree with, in order to achieve a practical and secure
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interchange system.
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</para>
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<sect2 id="configurations-dialup-usage-conn">
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<title>Establishing Dial-Up Connections</title>
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<para>
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To establish a dial-up connection to the server computer you
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need to install and configure a Modem device in your client
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computer. Each operating system has its own way of doing
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this, but if you are using &TC;;, you can use the
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<command>wvdialconf</command> and
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<command>system-config-network</command> commands, as
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described in <xref linkend="configurations-dialup-modem" />.
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</para>
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<para>
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In the configuration process you need to enter the following
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information:
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</para>
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<screen>
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ISP Name: server.example.com
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ISP Phone: +53043515094
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Username: client.example.com
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Password: mail4u
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</screen>
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</sect2>
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<sect2 id="configurations-dialup-usage-connlimits">
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<title>Administering Dial-Up Connections</title>
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<para>
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The lifetime of dial-up connections must be limitted based on
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the number of users you expect to establish connection and the
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kind of services you plan to provide. Using the information
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described in <xref linkend="configurations-dialup-server" />
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as reference, the lifetime of dial-up connections will be 15
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minutes from the moment they were established on. Likewise,
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once the connection has been established, if the link is idle
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for 1 minute, the server computer will close the connection to
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free the telephone line for others to use.
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</para>
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<para>
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The number of consecutive connections realized from the same
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telephone number in a fixed period of time must be also
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controlled in order to reduce Denial of Service (DoS) attacks.
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This way, you can consider an environment where: more than 3
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consecutive connections (that last 15 or less minutes each)
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from the same telephone number in a time range of 60 minutes
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will be taken as a DoS attack from the client computer. In
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such cases, once the client computer is disconnected from
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server computer, the telephone number originating the call
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won't be able to establish any further connection to the
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server computer in the next 15 minutes since the last it was
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disconnected on.
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</para>
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<note>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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In order to achieve an acceptable degree of efficiency when
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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controlling consecutive connections from the same telephone
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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number, it is required that both the client's telephone number
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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and connection times (e.g., when the connection was opened,
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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and when it was closed) be registered somehow in the server
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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computer (e.g., Is it on pppd's log file?). Without such
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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information it would be very difficult to achieve any
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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prevention against DoS attacks originated from incoming calls.
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</note>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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Another issue to consider here is that, in order to realize
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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any control over incoming telephone calls, it is required that
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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the client computer realizes a telepohne call into the server
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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computer to provide the telephone number information and that
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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certainly occupies the telephone line until the access control
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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actions take place. This could be used by evil users to
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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generate DoS attacks (e.g., by configuring a client computer
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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to redial the server computer telephone number forever), since
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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there is no way to control access at a Modem level without
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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occupying the telephone line for a few seconds at least. The
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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only change legitimate users have against such evil users'
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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attacks would be establish connection before them (e.g., in
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the exact range of time between disconnection and redial).
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</sect2>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<sect2 id="configurations-dialup-usage-users">
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<title>Administering User Profiles</title>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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In order for a you to use any service provided by the server
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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computer it is required that you get registered a user profile
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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first. The user profile provides the user information required
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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by services inside the server computer (e.g., username,
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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password, e-mail address, telephone number, etc.). To register
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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new user profiles, you need to use the web application
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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provided by the server computer. For example, assuming the
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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domain name of the server computer is
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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class="domainname">example.com</systemitem>, the URL of the
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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web application would be:
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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url="https://example.com/people/?action=register" />.
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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To reach the web interface, the first thing you need to do is
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
establishing a dial-up connection to the server computer as
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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described in
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linkend="configurations-dialup-usage-conn"/>. Once the dial-up
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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connection has been established, you need to open a web
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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browser (e.g., Firefox) and put the URL mentioned above in the
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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address space, and press Enter to go. This will present you a
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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list of instructions that will guide you through the
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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self-registration process. Other actions like updating or
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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deleting your user profile can be also achieved from this web
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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interface.
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
</para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<important>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<para>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
The web interface used to manage user profiles inside the
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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server computer must be presented over an encrypted session in
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
order to protect all the information passing through.
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</important>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<para>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
Inside the server computer, all related subsystems in need of
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
user information (e.g., Postix, Cyrus-Imapd and Saslauthd)
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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retrive user information from one single (LDAP) source. The
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
web application provided by the server computer manages all
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
these subsystems' configuration files in order to provide a
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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pleasant experience for end users. The web interface must be
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
as simple as possible in order to achieve all administration
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
tasks in the range of time permitted by the server computer
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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before it closes the connection established from the client
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
computer.
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</para>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<para>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
More information about the web interface you need to use to
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
manage your user profile inside the server computer can be
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
found in <xref linkend="administration-mail" />.
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</sect2>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<sect2 id="configurations-dialup-usage-scope">
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<title>Determining Information Scope</title>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<para>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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The information generated inside the server computer is
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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isolated from Internet. This way, any information generated
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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inside the server computer will be available only to people
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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registered inside the server computer. For example, don't ever
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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expect to send/receive e-mails to/from Internet e-mail
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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accounts like Gmail or Yahoo, nor visiting web sites like
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<ulink url="http://www.google.com/">Google</ulink> or
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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url="http://www.wikipedia.org/">Wikipedia</ulink> either. For
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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this to happen, it is required an established connection
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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between the server computer we are configuring and the
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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Internet network we want those services in, but such
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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established connection isn't possible in the current
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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environment.
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</para>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</sect2>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<sect2 id="configurations-dialup-usage-services">
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<title>Determining Provided Services</title>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<para>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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The implementation of services that required persistent
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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connections (e.g., <application>chats</application>) will not
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
be considered as a practical offer inside the server computer.
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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Instead, only asynchronous services (e.g.,
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<application>e-mail</application>) will be supported. This
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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restriction is required to reduce the amount time demanded by
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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services. For example, consider an environment where you
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
connect to the server computer for sending/receiving e-mails
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
messages and then quickly disconnect from it to free the
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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telephone line for others to use. In this environment, there
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
is no need for you and other person to be both connected at
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
the same time to send/receive e-mail messages to/from each
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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other. The e-mails sent from other person to you will be
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
available in your mailbox the next time you get connected to
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
the server computer and use your e-mail client to send/receive
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
e-mail messages. Likewise, you don't need to be connected to
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
the server computer in order to write your e-mail messages.
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
You can write down your messages off-line and then establish
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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connection once you've finished writing, just to send them
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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out and receive new messages that could have been probably
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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sent to you.
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
</para>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<para>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
Another issue related to e-mail exchange is the protocol used
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
to receive messages. Presently, there are two popular ways to
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
do this, one is through IMAP and another through POP3. When
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
you use IMAP protocol, e-mail messages are retained in the
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
server computer and aren't downloaded to client computer.
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
Otherwise, when you use POP3 protocol, e-mail messages are
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
downloaded to the client computer and removed from server
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
computer. Based on the resources we have and the kind of link
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
used by the client computer to connect the server computer,
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
using POP3 is prefered than IMAP. However both are made
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
available.
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
</para>
|
|
![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<para>
|
|
![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
Assuming you use IMAP protocol to read your mailbox, be aware
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
that you need to be connected to the server computer. Once
|
|
![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
the connection is lost you won't be able to read your messages
|
|
![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
(unless your e-mail client possesses a feature that let you
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
reading messages off-line). Morover, you run the risk of get
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
your mailbox out of space. If your mailbox gets out of space,
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
new messages sent to you will not be deliver to your mailbox.
|
|
![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
Instead, they will be deferred for about 5 days hoping you
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
free the space in your mailbox to deliver them. If you don't
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
free space within this period of time, e-mail messages sent to
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
you will be bounced back to their senders.
|
|
![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
</para>
|
|
![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
<para>
|
|
![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
Otherwise, if you use POP3 protocol to read your mailbox, you
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
always keep your mailbox free to receive new e-mails messages
|
|
![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
and keep them for you until the next time you establish
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
connection with the server computer and download them to your
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
client computer using your e-mail client.
|
|
![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
d46962 |
</para>
|
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</sect2>
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<sect2 id="configuration-dialup-usage-diskspace">
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<title>Determining Disk Space Usage</title>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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Assuming you are providing a public service, it is required to
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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limit the maximum number of users registered inside the server
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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computer, based on the maximum disk space the server computer
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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confines to such purpose. For example, consider an environment
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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where users can get registered themselves using a web
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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interface which requires the web application to know how much
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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free space is available before proceeding to register new mail
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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accounts inside the server computer; this, to prevent user
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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registrations when there isn't enough free space to perform a
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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new user registration. Considering the computer server has
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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confined 5GB of disk space to handle the mail service (e.g.,
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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mail queues, mailboxes, etc.), if we set 10MB for each user
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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account, it will be possible to provide self-registration
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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through the web interface for 500 users in total.
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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</para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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<para>
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![](https://seccdn.libravatar.org/avatar/6547be6a776b3f31e43b7f4b6dd82ebcede0f2d11be196e3a70e28760a760a3c?s=16&d=retro) |
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Another measure related to disk space saving might be to
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remove unused user accounts and their related files (e.g.,
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mailboxes) from the server computer. For example, consider an
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environment where user accounts are automatically removed from
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the server computer when they don't establish a connection
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with the server computer in a period greater than 7 days since
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the last valid connection established to the server computer.
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Once the user account is removed, it is no longer functional
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of course, and the person whom lost the account will need to
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create a new one, assuming it want to have access back to the
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mail service inside the server computer.
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</para>
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</sect2>
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</sect1>
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