84 lines
5.6 KiB
HTML
84 lines
5.6 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Mail and Mail Exchanger records" />
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<meta name="abstract" content="Domain Name System (DNS) supports advanced mail routing through the use of Mail and Mail Exchanger (MX) records." />
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<meta name="description" content="Domain Name System (DNS) supports advanced mail routing through the use of Mail and Mail Exchanger (MX) records." />
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<meta name="DC.Relation" scheme="URI" content="rzakkconceptresourcerec.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2004, 2006" />
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<meta name="DC.Identifier" content="rzakkmailmx" />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<title>Mail and Mail Exchanger records</title>
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</head>
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<body id="rzakkmailmx"><a name="rzakkmailmx"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Mail and Mail Exchanger records</h1>
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<div><p>Domain Name System (DNS) supports advanced mail routing through
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the use of Mail and Mail Exchanger (MX) records.</p>
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<p>Mail and MX records are used by mail routing programs, such as Simple Mail
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Transfer Protocol (SMTP). The lookup table in DNS resource records contains
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the types of mail records that iSeries™ DNS supports.</p>
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<p>DNS includes information for sending electronic mail by using mail exchanger
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information. If the network is using DNS, an SMTP application does not deliver
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mail addressed to host TEST.IBM.COM by opening a TCP connection to TEST.IBM.COM.
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SMTP first queries the DNS server to find out which host servers can be used
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to deliver the message.</p>
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<div class="section"><h4 class="sectiontitle">Deliver mail to a specific address</h4><p>DNS servers use
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resource records that are known as <em>mail exchanger</em> (MX) records. MX
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records map a domain or host name to a preference value and host name. MX
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records are generally used to designate that one host is used to process mail
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for another host. The records are also used to designate another host to deliver
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mail to, if the first host cannot be reached. In other words, they allow mail
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that is addressed to one host to be delivered to a different host.</p>
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<p>Multiple
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MX resource records might exist for the same domain or host name. When multiple
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MX records exist for the same domain or host, the preference (or priority)
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value of each record determines the order in which they are tried. The lowest
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preference value corresponds to the most preferred record, which is tried
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first. When the most preferred host cannot be reached, the sending mail application
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tries to contact the next, less preferred MX host. The domain administrator,
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or the creator of the MX record, sets the preference value.</p>
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<p>A DNS server
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can respond with an empty list of MX resource records when the name is in
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the DNS server's authority but has no MX assigned to it. When this occurs,
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the sending mail application might try to establish a connection with the
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destination host directly.</p>
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<div class="note"><span class="notetitle">Note:</span> Using a wild card (example: <samp class="codeph">*.mycompany.com</samp>)
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in MX records for a domain is not suggested.</div>
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</div>
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<div class="section"><h4 class="sectiontitle">Example: MX record for a host</h4><p>In the following example,
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the system, by preference, delivers mail for fsc5.test.ibm.com to the host
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itself. If the host cannot be reached, the system might deliver the mail to
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psfred.test.ibm.com or to mvs.test.ibm.com (if psfred.test.ibm.com also cannot
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be reached). This is an example of what these MX records will look like:</p>
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<pre> fsc5.test.ibm.com IN MX 0 fsc5.test.ibm.com
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IN MX 2 psfred.test.ibm.com
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IN MX 4 mvs.test.ibm.com</pre>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzakkconceptparent.htm" title="This topic explains what Domain Name System (DNS) is and how it works. It also shows the different types of zones that can be defined on a DNS server.">Domain Name System concepts</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="rzakkconceptresourcerec.htm" title="This topic explains how resource records are used by Domain Name System (DNS). Resource records are used to store data about domain names and IP addresses. This topic contains a searchable list of resource records supported for OS/400 V5R1.">Domain Name System resource records</a></div>
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</div>
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</div>
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</body>
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</html> |