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255 lines
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>Setup DNS records for your iRedMail server</title>
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<link href="./css/markdown.css" rel="stylesheet"></head>
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</head>
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<body>
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<div id="navigation">
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<a href="http://www.iredmail.org" target="_blank">iRedMail web site</a>
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// <a href="./index.html">Document Index</a>
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</div><h1 id="setup-dns-records-for-your-iredmail-server">Setup DNS records for your iRedMail server</h1>
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<div class="toc">
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<ul>
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<li><a href="#setup-dns-records-for-your-iredmail-server">Setup DNS records for your iRedMail server</a><ul>
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<li><a href="#a-record-for-server-hostname">A record for server hostname</a><ul>
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<li><a href="#what-is-an-a-record">What is an A record</a></li>
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<li><a href="#how-to-setup-an-a-record">How to setup an A Record</a></li>
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</ul>
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</li>
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<li><a href="#reverse-ptr-record-for-server-ip-address">Reverse PTR record for server IP address</a><ul>
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<li><a href="#what-is-a-reverse-ptr-record">What is a reverse PTR record</a></li>
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<li><a href="#why-do-you-need-a-reverse-ptr-record">Why do you need a reverse PTR record</a></li>
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<li><a href="#how-to-setup-a-reverse-ptr-record">How to setup a Reverse PTR record</a></li>
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</ul>
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</li>
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<li><a href="#mx-record-for-mail-domain-name">MX record for mail domain name</a><ul>
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<li><a href="#what-is-a-mx-record">What is a MX record</a></li>
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<li><a href="#how-to-setup-the-mx-record">How to setup the MX record</a></li>
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</ul>
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</li>
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<li><a href="#spf-record-for-your-mail-domain-name">SPF record for your mail domain name</a><ul>
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<li><a href="#what-is-a-spf-record">What is a SPF record</a></li>
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<li><a href="#how-to-setup-the-spf-record">How to setup the SPF record</a></li>
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</ul>
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</li>
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<li><a href="#dkim-record-for-your-mail-domain-name">DKIM record for your mail domain name</a><ul>
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<li><a href="#what-is-a-dkim-record">What is a DKIM record</a></li>
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<li><a href="#how-to-setup-the-dkim-record">How to setup the DKIM record</a></li>
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</ul>
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</li>
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<li><a href="#references">References</a></li>
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</ul>
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</li>
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</ul>
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</div>
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<p><strong>NOTE: STILL WORKING IN PROGRESS</strong></p>
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<p><strong>IMPORTANT NOTE</strong>: <code>A</code>, <code>MX</code> records are required, <code>Reverse PTR</code>, <code>SPF</code> and
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<code>DKIM</code> are optional but strongly recommended. All in all, set them all up please.</p>
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<h2 id="a-record-for-server-hostname">A record for server hostname</h2>
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<h3 id="what-is-an-a-record">What is an A record</h3>
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<p><code>A</code> records map a FQDN (fully qualified domain name) to an IP address. This is
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usually the most often used record type in any DNS system. This is the DNS
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record you should add if you want to point a domain name to a web server.</p>
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<h3 id="how-to-setup-an-a-record">How to setup an A Record</h3>
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<ul>
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<li>
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<p><code>Name</code>: This will be the host for your domain which is actually a computer
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within your domain. Your domain name is automatically appended to your name.
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If you are trying to make a record for the system <code>www.mydomain.com</code>. Then all
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you enter in the textbox for the name value is <code>www</code>.</p>
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<p><strong>Note</strong>: If you leave the name field blank it will default to be the record
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for your base domain <code>mydomain.com</code>. The record for your base domain is
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called the root record or apex record.</p>
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</li>
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<li>
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<p><code>IP</code>: The IP address of your FQDN. An IP address can be thought of as
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the telephone number to your computer. It is how one computer knows how to
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reach another computer. Similar to the country codes, area codes, and phone
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number it is used to call someone.</p>
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</li>
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<li>
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<p><code>TTL</code>: The TTL (Time to Live) is the amount of time your record will stay
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in cache on systems requesting your record (resolving nameservers, browsers,
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etc.). The TTL is set in seconds, so 60 is one minute, 1800 is 30 minutes, etc..</p>
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</li>
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</ul>
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<p>Systems that have a static IP should usually have a TTL of 1800 or higher.
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Systems that have a dynamic IP should usually have a TTL of 1800 of less.</p>
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<p>The lower the TTL the more often a client will need to query the name servers
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for your host's (record's) IP address this will result in higher query traffic
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for your domain name. Where as a very high TTL can cause downtime when you
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need to switch your IPs quickly.</p>
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<p>Sample record:</p>
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<pre><code>NAME TTL TYPE DATA
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www.mydomain.com. 1800 A 192.168.1.2
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mail.mydomain.com. 1800 A 192.168.1.5
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</code></pre>
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<p>The end result of this record is that <code>www.mydomain.com</code> points to
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<code>192.168.1.2</code>, and <code>mail.mydomain.com</code> points to <code>192.168.1.5</code>.</p>
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<h2 id="reverse-ptr-record-for-server-ip-address">Reverse PTR record for server IP address</h2>
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<h3 id="what-is-a-reverse-ptr-record">What is a reverse PTR record</h3>
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<p>PTR record or more appropriately a reverse PTR record is a process of resolving
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an IP address to its associated hostname. This is the exact opposite of the
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process of resolving a hostname to an IP address (<code>A</code> record). Example, when you ping a
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name <code>mail.mydomain.com</code> it will get resolved to the ip address using the DNS
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to something like <code>192.168.1.5</code>. Reverse PTR record does the opposite; it looks
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up the hostname for the given IP address. In the example above the PTR record
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for IP address <code>192.168.1.5</code> will get resolved to <code>mail.mydomain.com</code>.</p>
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<h3 id="why-do-you-need-a-reverse-ptr-record">Why do you need a reverse PTR record</h3>
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<p>The most common use for looking up a PTR record is done by spam filters.
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Concept behind this idea is that fly by night spammers who send e-mails out
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using fake domains generally will not have the appropriate reverse PTR setup
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at the ISP DNS zone. This criterion is used by spam filters to detect spam. If
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your domain does not have an appropriate reverse PTR record setup then chances
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are email spam filtering softwares <strong>MIGHT</strong> block e-mails from your mail server.</p>
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<h3 id="how-to-setup-a-reverse-ptr-record">How to setup a Reverse PTR record</h3>
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<p>You would most likely need to contact your ISP and make a request to create a
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reverse PTR record for your mail server IP address. For example, if your mail
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server hostname is <code>mail.somedoamin.com</code> then ask your ISP to setup a reverse
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PTR record 192.168.1.5 (your internet public IP address) in their revesre DNS
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zone. Reverse DNS zones are handled by your ISP even though you may have your
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own forward lookup DNS zone that you manage.</p>
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<h2 id="mx-record-for-mail-domain-name">MX record for mail domain name</h2>
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<h3 id="what-is-a-mx-record">What is a MX record</h3>
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<p>Mail Exchanger Record or more commonly known as MX record is an entry in the
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DNS server of your domain that tells other mail servers where your mail server
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is located. When someone sends an e-mail to a user that exists on your mail
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server from the internet, MX provides the location or IP address where to send
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that e-mail. MX record is the location of your mail server that you have
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provided to the outside world via the DNS.</p>
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<p>Most mail servers generally have more than one MX record, meaning you could
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have more than one mail server setup to receive e-mails. Each MX record has a
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priority number assigned to it in the DNS. The MX record with <strong>lowest number
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has the highest priority</strong> and that is considered your primary MX record or
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your main mail server. The next lowest mx number has the next highest primary
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and so on. You generally have more than one mail server, one being the primary
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and the others as backups, only one MX for mail server is OK too.</p>
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<h3 id="how-to-setup-the-mx-record">How to setup the MX record</h3>
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<p>If your ISP or domain name registrar is providing the DNS service, you can
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request them to set one up for you. If you manage your own DNS servers then
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you need to create the MX records in your DNS zone yourself.</p>
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<p>Sample MX record:</p>
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<pre><code>NAME PRIORITY TYPE DATA
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mydomain.com. 10 mx mail.mydomain.com
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</code></pre>
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<p>The end result of this record is, emails sent to <code>[user]@mydomain.com</code> will
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be delivered to server <code>mail.mydomain.com</code>.</p>
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<h2 id="spf-record-for-your-mail-domain-name">SPF record for your mail domain name</h2>
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<h3 id="what-is-a-spf-record">What is a SPF record</h3>
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<p>SPF is a spam and phishing scam fighting method which uses DNS SPF-records to
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define which hosts are permitted to send e-mails for a domain. For details on
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SPF, please see <a href="http://www.openspf.org/">http://www.openspf.org/</a></p>
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<p>This works by defining a DNS SPF-record for the e-mail domain name specifying
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which hosts (e-mail servers) are permitted to send e-mail from the domain name.</p>
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<p>Other e-mail servers can lookup this record when receiving an e-mail from this
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domain name to verify that sending e-mail server is connecting from a permitted
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IP address.</p>
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<h3 id="how-to-setup-the-spf-record">How to setup the SPF record</h3>
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<p>A new SPF-record type was recently added to the DNS protocol to support this
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(<a href="http://www.rfc-editor.org/rfc/rfc4408.txt">RFC4408</a>).</p>
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<p>However not all DNS and e-mail servers support this new record type yet, so
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SPF can also be configured in DNS using the TXT-record type.</p>
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<p>Examples:</p>
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<ul>
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<li>SPF record refer to MX record. It means emails sent from all servers defined
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in MX record of <code>mydomain.com</code> are permitted by sender organization.</li>
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</ul>
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<pre><code>mydomain.com. 3600 IN TXT "v=spf1 mx mx:mydomain.com -all"
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</code></pre>
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<ul>
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<li>or SPF record refer to IP address directly. it means emails sent from
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specified IP address are permitted by sender organization.</li>
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</ul>
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<pre><code>mydomain.com. 3600 IN TXT "v=spf1 ip4:192.168.1.100 -all"
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</code></pre>
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<p><code>-all</code> means prohibit all others.</p>
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<p>There're more valid mechanisms available, please check
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<a href="http://www.openspf.org/SPF_Record_Syntax">OpenSPF web site</a> for more details.</p>
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<h2 id="dkim-record-for-your-mail-domain-name">DKIM record for your mail domain name</h2>
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<h3 id="what-is-a-dkim-record">What is a DKIM record</h3>
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<p>DKIM allows an organization to take responsibility for a message in a way that
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can be verified by a recipient. The organization can be a direct handler of
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the message, such as the author's, the originating sending site's, or an
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intermediary's along the transit path. However, it can also be an indirect
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handler, such as an independent service that is providing assistance to a
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direct handler. DKIM defines a domain-level digital signature authentication
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framework for email through the use of public-key cryptography and using the
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domain name service as its key server technology
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(<a href="http://www.dkim.org/specs/rfc5585.html#RFC4871">RFC4871</a>). It permits
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verification of the signer of a message, as well as the integrity of its
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contents. DKIM will also provide a mechanism that permits potential email
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signers to publish information about their email signing practices; this will
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permit email receivers to make additional assessments of unsigned messages.
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DKIM's authentication of email identity can assist in the global control of
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"spam" and "phishing".</p>
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<p>A person or organization has an "identity" -- that is, a constellation of
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characteristics that distinguish them from any other identity. Associated
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with this abstraction can be a label used as a reference, or "identifier".
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This is the distinction between a thing and the name of the thing. DKIM uses
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a domain name as an identifier, to refer to the identity of a responsible
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person or organization. In DKIM, this identifier is called the Signing Domain
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IDentifier (SDID) and is contained in the DKIM-Signature header fields <code>d=</code>
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tag. Note that the same identity can have multiple identifiers.</p>
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<h3 id="how-to-setup-the-dkim-record">How to setup the DKIM record</h3>
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<ul>
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<li>Run command in terminal to show your DKIM keys:</li>
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</ul>
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<pre><code class="bash"># amavisd showkeys
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dkim._domainkey.mydomain.com. 3600 TXT (
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"v=DKIM1; p="
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"MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDYArsr2BKbdhv9efugByf7LhaK"
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"txFUt0ec5+1dWmcDv0WH0qZLFK711sibNN5LutvnaiuH+w3Kr8Ylbw8gq2j0UBok"
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"FcMycUvOBd7nsYn/TUrOua3Nns+qKSJBy88IWSh2zHaGbjRYujyWSTjlPELJ0H+5"
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"EV711qseo/omquskkwIDAQAB")
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</code></pre>
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<p><strong>Note</strong>: On some Linux/BSD distribution, you should use command <code>amavisd-new</code>
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instead of <code>amavisd</code>. if it complains <code>/etc/amavisd.conf not found</code>, you should
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tell amavisd the correct path of its config file. For example:</p>
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<pre><code class="shell"># amavisd -c /etc/amavisd/amavisd.conf showkeys
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</code></pre>
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<ul>
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<li>Copy output of above command into one line, like below. It will be the value
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of DKIM DNS record.</li>
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</ul>
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<pre><code>v=DKIM1; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDYArsr2BKbdhv9efugBy...
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</code></pre>
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<pre><code>__Note__: BIND ([The most widely used Name Server Software](http://www.isc.org/downloads/bind/))
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can handle this kind of multi-line format, so you can paste it in your domain
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zone file directly.
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</code></pre>
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<ul>
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<li>
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<p>Add a <code>TXT</code> type DNS record, set value to the line you copied above:
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<code>v=DKIM1; p=...</code>.</p>
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</li>
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<li>
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<p>After you added this in DNS, type below command to verify it:</p>
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</li>
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</ul>
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<pre><code class="shell"># amavisd testkeys
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TESTING: dkim._domainkey.mydomain.com => pass
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</code></pre>
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<p>If it shows <code>pass</code>, it works.</p>
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<p><strong>Note</strong>: If you use DNS service provided by ISP, new DNS record might take
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some hours to be available.</p>
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<h2 id="references">References</h2>
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<ul>
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<li><a href="http://en.wikipedia.org/wiki/MX_record">http://en.wikipedia.org/wiki/MX_record</a></li>
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<li><a href="http://www.openspf.org/">http://www.openspf.org/</a></li>
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<li><a href="http://www.dkim.org/">http://www.dkim.org/</a></li>
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</ul><br /><p style="text-align: center;">If you found something wrong
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in this document, please do
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<a href="http://www.iredmail.org/contact.html">contact us</a> to fix it.</p><p style="text-align: center; color: grey;">©© Creative Commons</p></body></html> |