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<h1>SPF</h1>
<p>From <a href="https://en.wikipedia.org/wiki/Sender_Policy_Framework">Wikipedia</a>:</p>
<div class="admonition quote">
<p class="admonition-title">Quote</p>
<p>Sender Policy Framework (SPF) is a simple email-validation system designed to detect email spoofing by providing a mechanism to allow receiving mail exchangers to check that incoming mail from a domain comes from a host authorized by that domain's administrators. The list of authorized sending hosts for a domain is published in the Domain Name System (DNS) records for that domain in the form of a specially formatted TXT record. Email spam and phishing often use forged "from" addresses, so publishing and checking SPF records can be considered anti-spam techniques.</p>
</div>
<div class="admonition seealso">
<p class="admonition-title">Seealso</p>
<p>For a more technical review: <a href="https://github.com/internetstandards/toolbox-wiki/blob/master/SPF-how-to.md">https://github.com/internetstandards/toolbox-wiki/blob/master/SPF-how-to.md</a></p>
</div>
<h2 id="add-a-spf-record"><a class="toclink" href="#add-a-spf-record">Add a SPF Record</a></h2>
<p>To add a SPF record in your DNS, insert the following line in your DNS zone:</p>
<div class="highlight"><pre><span></span><code>; MX record must be declared for SPF to work
domain.com. IN MX 1 mail.domain.com.
; SPF record
domain.com. IN TXT &quot;v=spf1 mx ~all&quot;
</code></pre></div>
<p>This enables the <em>Softfail</em> mode for SPF. You could first add this SPF record with a very low TTL.<br />
<em>SoftFail</em> is a good setting for getting started and testing, as it lets all email through, with spams tagged as such in the mailbox.</p>
<p>After verification, you <em>might</em> want to change your SPF record to <code>v=spf1 mx -all</code> so as to enforce the <em>HardFail</em> policy. See <a href="http://www.open-spf.org/SPF_Record_Syntax">http://www.open-spf.org/SPF_Record_Syntax</a> for more details about SPF policies.</p>
<p>In any case, increment the SPF record's TTL to its final value.</p>
<h2 id="backup-mx-secondary-mx"><a class="toclink" href="#backup-mx-secondary-mx">Backup MX, Secondary MX</a></h2>
<p>For whitelisting a IP Address from the SPF test, you can create a config file (see <a href="https://www.linuxcertif.com/man/5/policyd-spf.conf"><code>policyd-spf.conf</code></a>) and mount that file into <code>/etc/postfix-policyd-spf-python/policyd-spf.conf</code>.</p>
<p><strong>Example:</strong></p>
<p>Create and edit a <code>policyd-spf.conf</code> file here <code>/&lt;your docker-mailserver dir&gt;/config/postfix-policyd-spf.conf</code>:</p>
<div class="highlight"><pre><span></span><code><span class="na">debugLevel</span> <span class="o">=</span> <span class="s">1</span>
<span class="c1">#0(only errors)-4(complete data received)</span>
<span class="na">skip_addresses</span> <span class="o">=</span> <span class="s">127.0.0.0/8,::ffff:127.0.0.0/104,::1</span>
<span class="c1"># Preferably use IP-Addresses for whitelist lookups:</span>
<span class="na">Whitelist</span> <span class="o">=</span> <span class="s">192.168.0.0/31,192.168.1.0/30</span>
<span class="c1"># Domain_Whitelist = mx1.mybackupmx.com,mx2.mybackupmx.com</span>
</code></pre></div>
<p>Then add this line to <code>docker-compose.yml</code>:</p>
<div class="highlight"><pre><span></span><code><span class="nt">volumes</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./config/postfix-policyd-spf.conf:/etc/postfix-policyd-spf-python/policyd-spf.conf</span>
</code></pre></div>
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