210 lines
3.9 KiB
HTML
210 lines
3.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>Multiple Incoming Mail Exchangers</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Spam Filtering for Mail Exchangers"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Considerations"
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HREF="considerations.html"><LINK
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REL="PREVIOUS"
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TITLE="Considerations"
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HREF="considerations.html"><LINK
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REL="NEXT"
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TITLE="Blocking Access to Other SMTP Servers"
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HREF="otherservers.html"></HEAD
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><BODY
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CLASS="section"
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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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SUMMARY="Header navigation table"
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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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>Spam Filtering for Mail Exchangers: </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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HREF="considerations.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 3. Considerations</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="otherservers.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="section"
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><H1
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CLASS="section"
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><A
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NAME="multimx"
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></A
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>3.1. Multiple Incoming Mail Exchangers</H1
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><P
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> Most domains list more than one incoming <A
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HREF="gloss.html#mx"
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><I
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CLASS="glossterm"
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>Mail Exchanger</I
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></A
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>s
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(a.k.a. <SPAN
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CLASS="QUOTE"
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>"MX hosts"</SPAN
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>). If you do so, then bear in
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mind that in order to have any effect, any SMTP time filtering
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you incorporate on the primary MX has to be incorporated on all
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the others as well. Otherwise, the sending host would simply
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sidestep filtering by retrying the mail delivery through your
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backup server(s).
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</P
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><P
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> If the backup server(s) are not under your control, ask
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yourself whether you need multiple MXs in the first place. In
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this situation, chances are that they serve only as
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<EM
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>redundant</EM
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> mail servers, and that they in
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turn forward the mail to your primary MX. If so, you probably
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don't need them. If your host happens to be down for a little
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while, that's OK -- well-behaved sender hosts will retry
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deliveries for several days before giving up
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<A
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HREF="greylisting.html#FTN.noretrysenders"
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><SPAN
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CLASS="footnote"
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>[1]</SPAN
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></A
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>.
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</P
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><P
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> A situation where you <EM
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>may</EM
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> need multiple
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MXs is to perform load balancing between several servers -
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i.e. if you receive so much mail that one machine alone could
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not handle it. In this case, see if you could offload some
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tasks (such as <A
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HREF="datachecks.html#virusscanners"
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>virus</A
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> and
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<A
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HREF="datachecks.html#spamscanners"
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>spam</A
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> scanners) to other
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machines, in order to reduce or eliminate this need.
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</P
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><P
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> Again, if you do decide to keep using several MXs, your backup
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servers need to be (at least) as restrictive as the primary
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server, lest filtering in the primary MX is useless.
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</P
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><P
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> See also the section on <A
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HREF="greylisting.html"
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>Greylisting</A
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> for
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additional concerns related to multiple MX hosts.
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</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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SUMMARY="Footer navigation 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="considerations.html"
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ACCESSKEY="P"
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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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ACCESSKEY="H"
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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="otherservers.html"
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ACCESSKEY="N"
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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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>Considerations</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="considerations.html"
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ACCESSKEY="U"
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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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>Blocking Access to Other SMTP Servers</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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> |