234 lines
4.3 KiB
HTML
234 lines
4.3 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>Protecting Against Mail Spam</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.57"><LINK
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REL="HOME"
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TITLE="Linux Network Administrators Guide"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Getting EximUp and Running"
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HREF="x-087-2-exim.html"><LINK
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REL="PREVIOUS"
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TITLE="Message Routing and Delivery"
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HREF="x-087-2-exim.delivery.html"><LINK
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REL="NEXT"
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TITLE="UUCP Setup"
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HREF="x-087-2-exim.simple.html"></HEAD
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><BODY
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CLASS="SECT1"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>Linux Network Administrators Guide</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="x-087-2-exim.delivery.html"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 19. Getting EximUp and Running</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="x-087-2-exim.simple.html"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="AEN16298"
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>19.7. Protecting Against Mail Spam</A
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></H1
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><P
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>
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<TT
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CLASS="OPTION"
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>Mail spam</TT
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>, or unsolicited email advertising, is an
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annoying problem for many users. A project has been formed to address
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this problem called the Mail Abuse Protection System (MAPS), and a
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mechanism has been built that reduces the problem, called the Real
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Time Blackhole List (RBL). Information on how the MAPS RBL works can
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be obtained from its online documentation at <SPAN
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CLASS="SYSTEMITEM"
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>http://maps.vix.com/rbl/</SPAN
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>. The idea is
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simple. Sites that are caught generating mail spam are added into the
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database and mail transfer agents like Exim are able to query the
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database to confirm that a source is not a spammer before accepting
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mail from it.</P
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><P
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>Since the advent of the RBL, several other similar lists have been
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created. One of the most useful is the Dial-Up List (DUL), which lists
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the IP addresses of dial-up hosts. These should normally send outgoing
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mail only to their ISP's mail servers. Many sites block mail from
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external dial-ups because when such a host avoids its own ISP's
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server, it is usually up to no good.</P
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><P
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>Exim provides support for the real-time and other blacklists. It is
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very easily configured. To enable it, add the following lines to your
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<TT
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CLASS="FILENAME"
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>/etc/exim.conf</TT
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> file:</P
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><TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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># Vixie / MAPS RBL (http://maps.vix.com/rbl)
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rbl_domains = rbl.maps.vix.com : dul.maps.vix.com</PRE
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></TD
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></TR
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></TABLE
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><P
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>This example checks both the RBL and the DUL, rejecting any messages
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from hosts that are on either list. The <TT
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CLASS="OPTION"
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>rbl_hosts</TT
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>
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option allows you to specify groups of hosts to which RBL checking
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does (or does not) apply. The default setting is:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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>rbl_hosts = *</PRE
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></TD
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></TR
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></TABLE
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>
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which means that all hosts are subject to RBL checking. If you wanted to
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override blacklisting and accept mail from a specific host without
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performing the RBL checking you could, for example, use:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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>rbl_hosts = ! nocheck.example.com : *</PRE
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></TD
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></TR
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></TABLE
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>
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The exclamation mark before the first item in this list indicates a
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negated item: if the calling host is
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<SPAN
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CLASS="SYSTEMITEM"
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>nocheck.example.com</SPAN
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>,
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it will match this item. But because of the negation, RBL checking is
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not performed. Any other host matches the second item in the list. </P
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="x-087-2-exim.delivery.html"
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>Prev</A
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></TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="index.html"
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>Home</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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><A
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HREF="x-087-2-exim.simple.html"
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>Next</A
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></TD
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></TR
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><TR
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><TD
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WIDTH="33%"
|
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ALIGN="left"
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VALIGN="top"
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>Message Routing and Delivery</TD
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><TD
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WIDTH="34%"
|
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ALIGN="center"
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VALIGN="top"
|
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><A
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HREF="x-087-2-exim.html"
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>Up</A
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></TD
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><TD
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WIDTH="33%"
|
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ALIGN="right"
|
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VALIGN="top"
|
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>UUCP Setup</TD
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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> |