239 lines
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239 lines
9.0 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<META NAME="generator" CONTENT="lgazmail v1.3B.f">
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<TITLE>The Answer Guy 50: Mystery Question</TITLE>
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<H4>"The Linux Gazette...<I>making Linux just a little more fun!</I>"</H4>
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<P> <hr> <P>
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<center>
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<H1><A NAME="answer">
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<img src="../../gx/dennis/qbubble.gif" alt="(?)"
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border="0" align="middle">
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<font color="#B03060">The Answer Guy</font>
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<img src="../../gx/dennis/bbubble.gif" alt="(!)"
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border="0" align="middle">
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</A></H1>
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<BR>
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<H4>By James T. Dennis,
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<a href="mailto:linux-questions-only@ssc.com">linux-questions-only@ssc.com</a><BR>
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LinuxCare,
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<A HREF="http://www.linuxcare.com/">http://www.linuxcare.com/</A>
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</H4>
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</center>
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<p><hr><p>
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<!-- begin 45 -->
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<H3 align="left"><img src="../../gx/dennis/qbubble.gif"
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height="50" width="60" alt="(?) " border="0"
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>Mystery Question</H3>
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<p><strong>From Robert Polk on Thu, 20 Jan 2000
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</strong></p>
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<!-- ::
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Mystery Question
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~~~~~~~~~~~~~~~~
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:: -->
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<P><STRONG>
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Hello,
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</STRONG></P>
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<P><STRONG>
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Currently I am contracting for an LA based company. We currently
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have internal mail as well as a majority of users still using POP
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mail from an ISP.
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</STRONG></P>
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<P><STRONG>
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We'll say the domain name is <tt>z.com</tt>. My question is in regard to
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MX records.
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</STRONG></P>
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<P><STRONG>
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Example: <tt>domain z.com</tt>
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</STRONG></P>
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<pre><strong> MX preference 10 external.z.com
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MX preference 10 mail.z.com
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</strong></pre>
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<P><STRONG>
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then it continues with 20, etc preferences.
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</STRONG></P>
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<P><STRONG>
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Currently most users are still using this external mail for their
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internet email (<tt>external.z.com</tt>). There are however, about 20
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users internally that are only using the internal mail host for
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their internet email (<tt>mail.z.com</tt>)=
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</STRONG></P>
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<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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>
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I'm not sure what the question is.
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</BLOCKQUOTE>
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<BLOCKQUOTE>
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There is a problem if you're using both of these hosts
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(mail.z.com and external.z.com) as POP servers for the one
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domain. Unless you're doing some sort of address rewriting
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or other mail routing on one or the other of these then any
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piece of mail for z.com could land on either of these hosts.
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Since each of them has equal MX values, and there are no
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lower MX values for the z.com domain, the mail that lands on
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one or the other will stay there.
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</BLOCKQUOTE>
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<BLOCKQUOTE>
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In general you don't want to have this ambiguity.
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The lowest MX for a given domain or subdomain should
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lead to one unique host. The secondaries and tertiaries
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can be ambiguous since they will all relay their mail
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to the lower MX hosts.
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</BLOCKQUOTE>
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<BLOCKQUOTE>
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You can do scaling in a few ways at the MTA level.
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For example you can have a big aliases file (DBM)
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or a set of NIS/NIS+ maps or an LDAP server to
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provide aliasing of recipients to specific POP
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servers. This can give provide a "flat" external
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mail profile (everyone is @z.com) while allowing
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you to scale to a much larger number of users
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than you could support on a single POP server.
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</BLOCKQUOTE>
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<BLOCKQUOTE>
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(This assumes also that you'll configure all
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the mail hubs to re-write outgoing mail to
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masquerade the From: and Return: addresses).
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</BLOCKQUOTE>
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<BLOCKQUOTE>
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Maybe the question you were asking is how to
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have your mail servers distinquish between
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the internal and external users. In that case,
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just use aliases. Mail that's <EM>addressed</EM> to
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"external.z.com" will ignore the z.com MX record.
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Likewise for any that's <EM>addressed</EM> to "mail.z.com"
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</BLOCKQUOTE>
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<BLOCKQUOTE>
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To understand this you must note the distinction
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between where hosts to which mail is SENT and those
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to which it is ADDRESSED. Mail is sent to a host
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according to it's MX records. What that host does
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with it depends on how it is addressed. If the
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mail is addressed to any of the names that are on
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on a hosts "whoami" list (the sendmail 'w' class)
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then rewriting, aliasing, and local delivery are
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performed.
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</BLOCKQUOTE>
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<BLOCKQUOTE>
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(I'm shamelessly limiting the MTA terminology
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here to that of 'sendmail' --- the various other
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MTAs have similar features and concepts).
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</BLOCKQUOTE>
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<BLOCKQUOTE>
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Anyway, I've said more than enough given that
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I have no idea of what your question really is.
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</BLOCKQUOTE>
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</BLOCKQUOTE>
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<!-- sig -->
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<!-- end 45 -->
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<!--startcut ======================================================= -->
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<P> <hr> <P>
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<H5 align="center"><a href="http://www.linuxgazette.com/copying.html"
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>Copyright ©</a> 2000, James T. Dennis
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<BR>Published in <I>The Linux Gazette</I> Issue 50 February 2000</H5>
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<H6 ALIGN="center">HTML transformation by
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<A HREF="mailto:star@starshine.org">Heather Stern</a> of
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Starshine Technical Services,
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<A HREF="http://www.starshine.org/">http://www.starshine.org/</A>
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</H6>
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