ispmail-workaround-org/dist/ispmail-bookworm/relaying-outgoing-emails-through-postfix/index.html
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</script> <ul class="top-level astro-3ii7xxms"> <li class="astro-3ii7xxms"> <details open class="astro-3ii7xxms"> <sl-sidebar-restore data-index="0"></sl-sidebar-restore> <summary class="astro-3ii7xxms"> <span class="group-label astro-3ii7xxms"> <span class="large astro-3ii7xxms">ISPmail for Debian 13</span> </span> <svg aria-hidden="true" class="caret astro-3ii7xxms astro-c6vsoqas" width="16" height="16" viewBox="0 0 24 24" fill="currentColor" style="--sl-icon-size: 1.25rem;"><path d="m14.83 11.29-4.24-4.24a1 1 0 1 0-1.42 1.41L12.71 12l-3.54 3.54a1 1 0 0 0 0 1.41 1 1 0 0 0 .71.29 1 1 0 0 0 .71-.29l4.24-4.24a1.002 1.002 0 0 0 0-1.42Z"/></svg> </summary> <ul class="astro-3ii7xxms"> <li class="astro-3ii7xxms"> <a href="/ispmail-trixie/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Start here</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/upgrading/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Upgrading from Debian Bookworm</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/install-debian/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Installing Debian</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/install-the-software-packages/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Install software packages</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/virtual-domains/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Virtual domains</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/database/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Database setup</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/overview/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Big picture</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/dns-records/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">DNS records</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/tls-certificate/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">TLS certificate</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/postfix/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Postfix</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/dovecot/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Dovecot</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/lmtp/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">LMTP</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/webmail/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Webmail using Roundcube</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/relaying/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Sending / Relaying</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/imap/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">IMAP</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/managing-users-aliases-and-domains/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Managing users, aliases and domains</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/catching-spam-with-rspamd/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Catching spam with rspamd</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/anti-spoofing-dkim-spf/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Prevent spoofing using DKIM and SPF</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/catch-all/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Catch-all addresses</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/quotas/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Quotas</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/going-live/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Going live</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-trixie/automated-installation/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Automated installation</span> </a> </li> </ul> </details> </li><li class="astro-3ii7xxms"> <details open class="astro-3ii7xxms"> <sl-sidebar-restore data-index="1"></sl-sidebar-restore> <summary class="astro-3ii7xxms"> <span class="group-label astro-3ii7xxms"> <span class="large astro-3ii7xxms">ISPmail for Debian 12</span> </span> <svg aria-hidden="true" class="caret astro-3ii7xxms astro-c6vsoqas" width="16" height="16" viewBox="0 0 24 24" fill="currentColor" style="--sl-icon-size: 1.25rem;"><path d="m14.83 11.29-4.24-4.24a1 1 0 1 0-1.42 1.41L12.71 12l-3.54 3.54a1 1 0 0 0 0 1.41 1 1 0 0 0 .71.29 1 1 0 0 0 .71-.29l4.24-4.24a1.002 1.002 0 0 0 0-1.42Z"/></svg> </summary> <ul class="astro-3ii7xxms"> <li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Start here</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/whats-new/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">What&#39;s new</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/migrating-from-a-bullseye-to-a-bookworm-server/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Migrating from your old (Bullseye) server</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/big-picture/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">The big picture</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/types-of-email-domains/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Types of email domains</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/install-debian-bookworm-on-your-server/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Installing Debian</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/install-the-software-packages/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Install software packages</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/creating-a-tls-encryption-key-and-certificate/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">TLS certificate</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/prepare-the-database/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Preparing the database</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/making-postfix-get-its-information-from-the-mariadb-database/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Let Postfix access MariaDB</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/catchall-aliases/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Catch-all aliases</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/setting-up-dovecot/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Setting up Dovecot</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/let-postfix-send-emails-to-dovecot/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Let Postfix send emails to Dovecot</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/quotas/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Quotas</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/testing-imap/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Testing IMAP</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/webmail-using-roundcube/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Webmail using Roundcube</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/testing-email-delivery/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Testing email delivery</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/relaying-outgoing-emails-through-postfix/" aria-current="page" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Relaying outgoing emails through Postfix</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/catching-spam-with-rspamd/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Catching spam with rspamd</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/setting-dns-records/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Setting DNS records</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/prevent-spoofing-using-dkim/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Prevent spoofing using DKIM</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/managing-users-aliases-and-domains/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Managing users, aliases and domains</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/monitoring-and-backup/" aria-current="false" class="astro-3ii7xxms"> <span class="astro-3ii7xxms">Monitoring and Backup</span> </a> </li><li class="astro-3ii7xxms"> <a href="/ispmail-bookworm/automatic-installation-with-ansible/" aria-current="false" 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addresses</span> </a> </li> </ul> </nav></starlight-toc><script type="module" src="/_astro/TableOfContents.astro_astro_type_script_index_0_lang.CKWWgpjV.js"></script></div></div> </div> </aside> <div class="main-pane astro-67yu43on"> <main data-pagefind-body class="astro-bguv2lll" lang="en" dir="ltr"> <section style="background-color: #ffefef; padding: 1rem; border: 1px solid #f00; text-align: center;" class="astro-kggsjsm4">
⚠️ This page is part of the ISPmail guide for Debian Bookworm. Please use the newer guide for <a href="/ispmail-trixie/" class="astro-kggsjsm4">Debian Trixie</a>.
</section> <div class="content-panel astro-7nkwcw3z"> <div class="sl-container astro-7nkwcw3z"> <h1 id="_top" class="astro-j6tvhyss">Relaying outgoing emails through Postfix</h1> </div> </div> <div class="content-panel astro-7nkwcw3z"> <div class="sl-container astro-7nkwcw3z"> <div class="sl-markdown-content"> <div class="sl-heading-wrapper level-h2"><h2 id="relaying">Relaying</h2><a class="sl-anchor-link" href="#relaying"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “Relaying”</span></a></div>
<p>Your mail server is almost ready for use. But one puzzle piece is missing. Your users can receive emails but they cannot send them yet.</p>
<p>Please note that there is a difference on how <strong>users</strong> send emails versus how <strong>servers</strong> send emails. For comparison:</p>
<ul>
<li>A <strong>mail server</strong> fetches the <em>MX</em> record for the domain name of the recipients email address. That tells it which mail server to talk to. Then it opens an SMTP connection (TCP port 25) and sends the email.</li>
<li>An <strong>end user</strong> with a mail client like Thunderbird, Evolution or Mutt cannot do it this way. The mail clients have no functionality built in for that <em>MX</em> record fetching magic. And the user is most likely on a <em>dynamic IP address</em> that other mail servers do not trust and reject. End users are meant to send emails to their providers (your!) mail server, send login information to authenticate themselves and then send the email. This is called <em>relaying</em> because your mail server acts as a <em>relay</em> between the user and other mail servers on the internet. For security reasons the user also has to authenticate to be allowed to send emails.</li>
</ul>
<p>I created a couple of illustrations to explain it.</p>
<div class="sl-heading-wrapper level-h3"><h3 id="incoming-email">Incoming email</h3><a class="sl-anchor-link" href="#incoming-email"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “Incoming email”</span></a></div>
<p>When someone on the internet sends an email to <code dir="auto">john@example.org</code>, some other mail server will deliver the email using SMTP to your mail server. Postfix will determine that its responsible for email addresses in the example.org domain and accept the email. John can then get the email from your server.</p>
<p><img src="/_astro/relaying-incoming-email.DZJIOHqZ_29Vv5S.webp" alt="Diagram that shows an email coming into Postfix" loading="lazy" decoding="async" fetchpriority="auto" width="519" height="126"></p>
<div class="sl-heading-wrapper level-h3"><h3 id="outgoing-email-without-authentication">Outgoing email (without authentication)</h3><a class="sl-anchor-link" href="#outgoing-email-without-authentication"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “Outgoing email (without authentication)”</span></a></div>
<p>John is on the internet somewhere and wants to send an email to <a href="mailto:lisa@example.com">lisa@example.com</a>. Your mail server is not responsible for the “example.com” domain so it receives Johns email and would have to forward (relay) it to the actual mail server that is responsible for …@example.com email addresses. This may seem like a harmless scenario but your mail server must deny that:</p>
<p><img src="/_astro/relaying-unauthenticated-relaying-denied.Luyv3w4j_2eyNO1.webp" alt="Diagram that shows an outgoing unauthenticated email getting rejected" loading="lazy" decoding="async" fetchpriority="auto" width="317" height="97"></p>
<p>Why? Because anyone can claim to be John and make your mail server forward mail. If an attacker (like a spammer) would send millions of spam emails in Johns name through your server then other organisations will accuse <em>you</em> as the operator of the mail server of spamming. Your mail server would be what people call an <em><a href="https://en.wikipedia.org/wiki/Open_mail_relay">open relay</a></em>. That is not what you want because your mail server would get blacklisted and you will not be able to send out mail to most other servers. So without any proof that the sender is indeed John, your server must reject the email.</p>
<div class="sl-heading-wrapper level-h3"><h3 id="outgoing-email-with-authentication">Outgoing email (with authentication)</h3><a class="sl-anchor-link" href="#outgoing-email-with-authentication"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “Outgoing email (with authentication)”</span></a></div>
<p>So how does John prove his identity? He needs to use <em>authenticated</em> SMTP. This is similar to the previous case but Johns email program will also send his username and password.</p>
<p><img src="/_astro/relaying-authenticated-relaying.D-QXvHmY_ZDn7Cs.webp" alt="Diagram that shows an outgoing authenticated email getting relayed" loading="lazy" decoding="async" fetchpriority="auto" width="501" height="110"></p>
<p>We are making sure that his authentication happens over an encrypted connection so Johns password is safe.</p>
<div class="sl-heading-wrapper level-h2"><h2 id="postfix-setting-mynetworks">Postfix setting “mynetworks”</h2><a class="sl-anchor-link" href="#postfix-setting-mynetworks"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “Postfix setting “mynetworks””</span></a></div>
<p>In addition to using SMTP authentication you can tell Postfix to always allow relaying for certain IP addresses. The <em>mynetworks</em> setting contains the list of IP networks or IP addresses that you trust. Usually you define your own local network here. The reason John had to authenticate in the above example is because his IP address is not part of <em>mynetworks</em>.</p>
<div class="sl-heading-wrapper level-h2"><h2 id="make-postfix-use-dovecot-for-authentication">Make Postfix use Dovecot for authentication</h2><a class="sl-anchor-link" href="#make-postfix-use-dovecot-for-authentication"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “Make Postfix use Dovecot for authentication”</span></a></div>
<p>Enabling SMTP authentication in Postfix is surprisingly easy. You already configured Dovecot so it knows all about your users from the SQL database. So lets just make Postfix use that by telling it to ask the Dovecot server to verify the username and password. Postfix just needs some extra configuration. Run these commands on the shell:</p>
<div class="expressive-code"><link rel="stylesheet" href="/_astro/ec.v4551.css"><script type="module" src="/_astro/ec.0vx5m.js"></script><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">postconf smtpd_sasl_type=dovecot</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">postconf smtpd_sasl_path=private/auth</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">postconf smtpd_sasl_auth_enable=yes</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="postconf smtpd_sasl_type=dovecotpostconf smtpd_sasl_path=private/authpostconf smtpd_sasl_auth_enable=yes"><div></div></button></div></figure></div>
<p>This enables SMTP authentication and tells Postfix that it can talk to Dovecot through a socket file located at <code dir="auto">/var/spool/postfix/private/auth</code>. Do you remember that Postfix runs in a sandboxed <em>chroot</em> directory? Thats at /var/spool/postfix. It cannot access any files outside of that directory. But fortunately in a previous section you edited the /etc/dovecot/conf.d/10-master.conf file and made Dovecot place a socket file into <code dir="auto">/var/spool/postfix/private/auth</code> to allow communication from Postfix.</p>
<div class="sl-heading-wrapper level-h2"><h2 id="enable-encryption">Enable encryption</h2><a class="sl-anchor-link" href="#enable-encryption"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “Enable encryption”</span></a></div>
<p>The following settings enable encryption, set the key and certificate paths for Postfix. Just run these commands:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">postconf smtpd_tls_security_level=may</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">postconf smtpd_tls_auth_only=yes</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">postconf smtpd_tls_cert_file=/etc/letsencrypt/live/webmail.example.org/fullchain.pem</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">postconf smtpd_tls_key_file=/etc/letsencrypt/live/webmail.example.org/privkey.pem</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">postconf smtp_tls_security_level=may</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="postconf smtpd_tls_security_level=maypostconf smtpd_tls_auth_only=yespostconf smtpd_tls_cert_file=/etc/letsencrypt/live/webmail.example.org/fullchain.pempostconf smtpd_tls_key_file=/etc/letsencrypt/live/webmail.example.org/privkey.pempostconf smtp_tls_security_level=may"><div></div></button></div></figure></div>
<aside aria-label="smtp or smtpd?" class="starlight-aside starlight-aside--tip"> <p class="starlight-aside__title" aria-hidden="true"> <svg aria-hidden="true" class="starlight-aside__icon astro-c6vsoqas" width="16" height="16" viewBox="0 0 24 24" fill="currentColor" style="--sl-icon-size: 1em;"><path fill-rule="evenodd" d="M1.44 8.855v-.001l3.527-3.516c.34-.344.802-.541 1.285-.548h6.649l.947-.947c3.07-3.07 6.207-3.072 7.62-2.868a1.821 1.821 0 0 1 1.557 1.557c.204 1.413.203 4.55-2.868 7.62l-.946.946v6.649a1.845 1.845 0 0 1-.549 1.286l-3.516 3.528a1.844 1.844 0 0 1-3.11-.944l-.858-4.275-4.52-4.52-2.31-.463-1.964-.394A1.847 1.847 0 0 1 .98 10.693a1.843 1.843 0 0 1 .46-1.838Zm5.379 2.017-3.873-.776L6.32 6.733h4.638l-4.14 4.14Zm8.403-5.655c2.459-2.46 4.856-2.463 5.89-2.33.134 1.035.13 3.432-2.329 5.891l-6.71 6.71-3.561-3.56 6.71-6.711Zm-1.318 15.837-.776-3.873 4.14-4.14v4.639l-3.364 3.374Z" clip-rule="evenodd"/><path d="M9.318 18.345a.972.972 0 0 0-1.86-.561c-.482 1.435-1.687 2.204-2.934 2.619a8.22 8.22 0 0 1-1.23.302c.062-.365.157-.79.303-1.229.415-1.247 1.184-2.452 2.62-2.935a.971.971 0 1 0-.62-1.842c-.12.04-.236.084-.35.13-2.02.828-3.012 2.588-3.493 4.033a10.383 10.383 0 0 0-.51 2.845l-.001.016v.063c0 .536.434.972.97.972H2.24a7.21 7.21 0 0 0 .878-.065c.527-.063 1.248-.19 2.02-.447 1.445-.48 3.205-1.472 4.033-3.494a5.828 5.828 0 0 0 .147-.407Z"/></svg>smtp or smtpd? </p> <div class="starlight-aside__content"> <p>Look closely. Some settings start with “smtp_” and others with “smtpd_”. That is not a typo. “smtp_” refers to the SMTP <em>client</em>. That is the component that sends out emails <strong>from</strong> Postfix <strong>to</strong> other servers.</p><p>Whereas “smtpd_” means the SMTP <em>server.</em> That in turn is the component that <strong>receives</strong> emails <strong>from</strong> other systems either from a remote mail server or one of your users.</p> </div> </aside>
<p>The above settings allow encrypted incoming (smtpd_) and outgoing (smtp_) connections. But they do not enforce it. If a remote mail server does not have encryption enabled we will still accept their emails. You may be tempted to enforce encryption but that would reject email communication with servers who have been configured without encryption.</p>
<p>However the <code dir="auto">smtpd_tls_auth_only=yes</code> setting makes sure that the users authentication information (email address and password) are always encrypted between the user and your mail server.</p>
<aside aria-label="Restrictions" class="starlight-aside starlight-aside--tip"> <p class="starlight-aside__title" aria-hidden="true"> <svg aria-hidden="true" class="starlight-aside__icon astro-c6vsoqas" width="16" height="16" viewBox="0 0 24 24" fill="currentColor" style="--sl-icon-size: 1em;"><path fill-rule="evenodd" d="M1.44 8.855v-.001l3.527-3.516c.34-.344.802-.541 1.285-.548h6.649l.947-.947c3.07-3.07 6.207-3.072 7.62-2.868a1.821 1.821 0 0 1 1.557 1.557c.204 1.413.203 4.55-2.868 7.62l-.946.946v6.649a1.845 1.845 0 0 1-.549 1.286l-3.516 3.528a1.844 1.844 0 0 1-3.11-.944l-.858-4.275-4.52-4.52-2.31-.463-1.964-.394A1.847 1.847 0 0 1 .98 10.693a1.843 1.843 0 0 1 .46-1.838Zm5.379 2.017-3.873-.776L6.32 6.733h4.638l-4.14 4.14Zm8.403-5.655c2.459-2.46 4.856-2.463 5.89-2.33.134 1.035.13 3.432-2.329 5.891l-6.71 6.71-3.561-3.56 6.71-6.711Zm-1.318 15.837-.776-3.873 4.14-4.14v4.639l-3.364 3.374Z" clip-rule="evenodd"/><path d="M9.318 18.345a.972.972 0 0 0-1.86-.561c-.482 1.435-1.687 2.204-2.934 2.619a8.22 8.22 0 0 1-1.23.302c.062-.365.157-.79.303-1.229.415-1.247 1.184-2.452 2.62-2.935a.971.971 0 1 0-.62-1.842c-.12.04-.236.084-.35.13-2.02.828-3.012 2.588-3.493 4.033a10.383 10.383 0 0 0-.51 2.845l-.001.016v.063c0 .536.434.972.97.972H2.24a7.21 7.21 0 0 0 .878-.065c.527-.063 1.248-.19 2.02-.447 1.445-.48 3.205-1.472 4.033-3.494a5.828 5.828 0 0 0 .147-.407Z"/></svg>Restrictions </p> <div class="starlight-aside__content"> <p>In the past you may have configured your <em>smtpd_recipient_restrictions</em> to restrict relaying to authenticated users. Postfix nowadays has setting called “<a href="http://www.postfix.org/postconf.5.html#smtpd_relay_restrictions">smtpd_relay_restrictions</a>” that deals with relaying requests in the “RCPT TO” phase of the SMTP dialog. So essentially it works like the good old “smtpd_recipient_restrictions” but is checked first. <em>smtpd_relay_restrictions</em> has a reasonable default so authenticated relaying works automatically:</p><p><code dir="auto">smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination</code></p> </div> </aside>
<div class="sl-heading-wrapper level-h3"><h3 id="how-smtpauthentication-works">How SMTP authentication works</h3><a class="sl-anchor-link" href="#how-smtpauthentication-works"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “How SMTP authentication works”</span></a></div>
<p>Are you curious how SMTP authentication looks on a low level? You probably are not. But lets do it anyway. Just once, so that you get the idea.</p>
<p>In previous versions of this guide we used “telnet” to connect to TCP port 25 and speak SMTP. But now we enforce encryption and cant do SMTP authentication unencrypted. Lets try it anyway:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">telnet localhost smtp</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="telnet localhost smtp"><div></div></button></div></figure></div>
<p>The server will let you in:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">Trying 127.0.0.1…</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">Connected to localhost.</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">Escape character is '^\]'.</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">220 webmail ESMTP Postfix (Debian/GNU)</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="Trying 127.0.0.1…Connected to localhost.Escape character is &#x27;^\]&#x27;.220 webmail ESMTP Postfix (Debian/GNU)"><div></div></button></div></figure></div>
<p>Say hello:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">ehlo example.com</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="ehlo example.com"><div></div></button></div></figure></div>
<p>Postfix will present a list of features that are available for you:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-mailtest</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-PIPELINING</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-SIZE 10240000</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-VRFY</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-ETRN</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-STARTTLS</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-ENHANCEDSTATUSCODES</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-8BITMIME</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-DSN</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-SMTPUTF8</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250 CHUNKING</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="250-mailtest250-PIPELINING250-SIZE 10240000250-VRFY250-ETRN250-STARTTLS250-ENHANCEDSTATUSCODES250-8BITMIME250-DSN250-SMTPUTF8250 CHUNKING"><div></div></button></div></figure></div>
<p>Let me briefly explain what these lines mean:</p>
<ul>
<li>PIPELINING<br>
This is a feature to speed up SMTP communication. Usually the remote system has to wait for a response to every command it sends. Pipelining allows the remote server to send several commands in a batch without waiting for a response. Postfix will just store these commands and execute them one by one. If you told Postfix to forbid pipelining it would disconnect the remote server when it tries to send bulks of commands without waiting for the proper reply. It is mainly a feature against rogue senders.</li>
<li>SIZE 10240000<br>
The remote server is allowed to send emails up to 10 MB large. This has long been a common maximum size for emails. However nowadays 40 MB or even more are more common sizes because emails have grown larger. Some mail servers even allow 100 MB.</li>
<li>VRFY<br>
Allows remote servers to verify a given name or email address. For example the remote server could send “VRFY john” and your server might respond <code dir="auto">250 John Doe &#x3C;john@example.org></code>. It can be used to verify that a certain recipient email address is deliverable</li>
<li>ETRN<br>
A command that a remote system can send to flush the Postfix queue of mails for a certain domain. It can be used if the remote system had technical problems and failed to receive email for a while. Then it could send an ETRN command to make your server start sending outstanding emails for that domain. It is rarely used.</li>
<li>STARTTLS<br>
This tells the remote system that it might start switching from this unencrypted to an encrypted connection by sending the “STARTTLS” command. It will then start negotiating a TLS-encrypted connection. You could compare it to an HTTP connection that suddenly switches over to an encrypted HTTPS connection. The advantage is that you can start talking SMTP on TCP port 25 and dont have to open up a second TCP port like 465 which is the “SSMTP” (secure SMTP) port and only accepts encrypted connections.</li>
<li>ENHANCEDSTATUSCODES<br>
This enables more three-digit return codes for various conditions. See the <a href="http://tools.ietf.org/html/rfc2034">RFC2034</a> if you are curious.</li>
<li>8BITMIME<br>
In ancient times SMTP only processed 7-bit characters. You couldnt transfer special characters like “Ä” or “ß” without special encoding. 8BITMIME allows a transmission of emails using 8-bit characters. Still many emails are specially encoded using ISO8859-1 or UTF-8.</li>
<li>DSN<br>
It enables DSNs (delivery status notofications) that allows the sender to control the messages that Postfix creates when an email could not be delivered as intended.</li>
<li>SMTPUTF8<br>
In addition to 8BITMIME you can use UTF8 encoded characters in header fields.</li>
<li>CHUNKING<br>
This feature (described in <a href="https://tools.ietf.org/html/rfc3030">RFC 3030</a>) makes sending of large emails more efficient.</li>
</ul>
<p>However one important line is missing here that would allow us to send our username and password:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-AUTH PLAIN LOGIN</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="250-AUTH PLAIN LOGIN"><div></div></button></div></figure></div>
<p>We told Postfix to only allow authentication when the connection is encrypted. So we are not offered authentication over this plain text connection. Thats what we want.</p>
<p>Are you still connected? Okay, good. So we need an encrypted connection using TLS. Using the STARTTLS feature we can switch over from unencrypted to encrypted without having to reconnect. Enter…</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">STARTTLS</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="STARTTLS"><div></div></button></div></figure></div>
<p>And the server replies:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">220 2.0.0 Ready to start TLS</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="220 2.0.0 Ready to start TLS"><div></div></button></div></figure></div>
<p>However now its getting weird because you would have to speak TLS encryption which is not a language that humans speak. So lets quit this using the “QUIT” command and do that differently:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">QUIT</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="QUIT"><div></div></button></div></figure></div>
<p>We can use OpenSSL to help us with the decryption. Run:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">openssl s_client -connect localhost:25 -starttls smtp</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="openssl s_client -connect localhost:25 -starttls smtp"><div></div></button></div></figure></div>
<p>You will see a lot of output. OpenSSL has connected to TCP port 25 and issued a STARTTLS command to switch to an encrypted connection. So whatever you type now will get encrypted. Enter:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">EHLO example.com</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="EHLO example.com"><div></div></button></div></figure></div>
<p>And Postfix will send a list of capabilities that will look like this:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-PIPELINING</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-SIZE 10240000</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-VRFY</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-ETRN</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-AUTH PLAIN LOGIN</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-ENHANCEDSTATUSCODES</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250-8BITMIME</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">250 DSN</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="250-PIPELINING250-SIZE 10240000250-VRFY250-ETRN250-AUTH PLAIN LOGIN250-ENHANCEDSTATUSCODES250-8BITMIME250 DSN"><div></div></button></div></figure></div>
<p>And now that we are using an encrypted connection Postfix offers us to authenticate. So let us send the authentication string with a Base64-encoded password:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">AUTH PLAIN AGpvaG5AZXhhbXBsZS5vcmcAc3VtbWVyc3Vu</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="AUTH PLAIN AGpvaG5AZXhhbXBsZS5vcmcAc3VtbWVyc3Vu"><div></div></button></div></figure></div>
<p>Unless you have changed Johns password to something else than “summersun” the server should accept that authentication:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">235 2.7.0 Authentication successful</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="235 2.7.0 Authentication successful"><div></div></button></div></figure></div>
<p>Excellent. You are logged in through SMTP. You could now send an email to be forwarded to another mail server. I just wanted to show that authentication works if you use an encrypted connection.</p>
<p>Disconnect from Postfix:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">QUIT</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="QUIT"><div></div></button></div></figure></div>
<p>Authentication works. Well done.</p>
<div class="sl-heading-wrapper level-h2"><h2 id="base64-encoded-passwords">Base64-encoded passwords</h2><a class="sl-anchor-link" href="#base64-encoded-passwords"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “Base64-encoded passwords”</span></a></div>
<p>Wait a minute. What was that crazy cryptic string? There was no username and password in it. Was it encrypted?</p>
<p>No, that was no encryption. It was merely an <em>encoded</em> version of the username and password. Why that? Well usually in SMTP you can only transfer ASCII characters. But the password may contain special characters which are not covered by ASCII. So in the <em>PLAIN</em> method that information is <a href="https://en.wikipedia.org/wiki/Base64">Base64</a> encoded.</p>
<p>What is actually converted to Base64…</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">NULL-BYTE + USERNAME + NULL-BYTE + PASSWORD</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="NULL-BYTE + USERNAME + NULL-BYTE + PASSWORD"><div></div></button></div></figure></div>
<p>So for Johns case you can easily create the Base64 string using:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">printf '\0john@example.org\0summersun' | base64</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="printf &#x27;\0john@example.org\0summersun&#x27; | base64"><div></div></button></div></figure></div>
<p>As a result you will get the exact same string you used above with “AUTH PLAIN”.</p>
<div class="sl-heading-wrapper level-h2"><h2 id="the-submission-port">The submission port</h2><a class="sl-anchor-link" href="#the-submission-port"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “The submission port”</span></a></div>
<p>Although I have been talking about SMTP on port 25 to relay mails, it is actually not the proper way. End users should not use port 25 but rather the <em>submission</em> service on TCP port 587 (as described in <a href="https://tools.ietf.org/html/rfc4409">RFC 4409</a>). The idea is to use port 25 for transporting email (<em>MTA = mail transport agent</em>) from server to server and port 587 for submitting (<em>MSA = mail submission agent</em>) email from a user to a mail server.</p>
<p>For comparison:</p>
<table><thead><tr><th>TCP Port</th><th>25</th><th>587</th></tr></thead><tbody><tr><td>Service name</td><td>SMTP</td><td>Submission</td></tr><tr><td>Encryption</td><td>Optional</td><td>Mandatory</td></tr><tr><td>Authentication</td><td>Optional</td><td>Mandatory</td></tr><tr><td>Meant for</td><td>Server-to-Server</td><td>User-to-Server</td></tr><tr><td>Your ISP</td><td>may block this port</td><td>should allows this port</td></tr></tbody></table>
<p>I hope that makes the distinction a bit clearer. So lets enable the <em>submission</em> service. All Postfix services are declared in the <code dir="auto">/etc/postfix/master.cf</code> file. Please edit the file and look for the <em>submission</em> section that is commented out by default. Turn that section into the following. Basically I removed the # character on all lines of this section and removed the lines with the mua_* variables.</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">submission inet n - y - - smtpd</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o syslog_name=postfix/submission</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o smtpd_tls_security_level=encrypt</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o smtpd_sasl_auth_enable=yes</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o smtpd_tls_auth_only=yes</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o smtpd_reject_unlisted_recipient=no</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o smtpd_client_restrictions=</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o smtpd_helo_restrictions=</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o smtpd_sender_restrictions=</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o smtpd_relay_restrictions=</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o smtpd_recipient_restrictions=permit_sasl_authenticated,reject</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o milter_macro_daemon_name=ORIGINATING</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="submission inet n - y - - smtpd -o syslog_name=postfix/submission -o smtpd_tls_security_level=encrypt -o smtpd_sasl_auth_enable=yes -o smtpd_tls_auth_only=yes -o smtpd_reject_unlisted_recipient=no -o smtpd_client_restrictions= -o smtpd_helo_restrictions= -o smtpd_sender_restrictions= -o smtpd_relay_restrictions= -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject -o milter_macro_daemon_name=ORIGINATING"><div></div></button></div></figure></div>
<p>Make sure to start the first line in the first column and indent the following lines.</p>
<p>This service uses the “smtpd” daemon (see the last word of the first line) which is the piece of software that responds if you open an SMTP connection on TCP port 25. But it gets a few extra options set…</p>
<ul>
<li>in the /var/log/mail.log log file you will see the connections to the submission port as “postfix/submission” (the <em>syslog_name</em> setting above)</li>
<li>enforce encryption on this port (<em>smtpd_tls_security_level</em>)</li>
<li>enable authentication (<em>smtpd_sasl_auth_enable</em>)</li>
<li>enforce encryption during authentication (<em>smtpd_tls_auth_only</em>)</li>
<li>allow sending emails to recipients outside of this mail server (<em>smtpd_reject_unlisted_recipient</em>)</li>
<li>remove special restrictions (<em>smtpd_*_restrictions</em>)</li>
<li>allow relaying if the sender was authenticated (<em>smtpd_recipient_restrictions</em>)</li>
<li>send the string <em>ORIGINATING</em> to milter services (<em>milter_macro_daemon_name</em>) you can just leave it like that</li>
</ul>
<p>Restart the Postfix server:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">systemctl restart postfix</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="systemctl restart postfix"><div></div></button></div></figure></div>
<p>Your users can now use the <em>submission</em> port to send email. They just use the port 587 in their mail clients instead of port 25.</p>
<p>Feel free to send a test mail using the submission port and encryption. You will need to install the libnet-ssleay-perl package first, so that SWAKS can speak TLS:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">apt install -y libnet-ssleay-perl</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">swaks --server localhost --to john@example.org \</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">--port 587 -tls \</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">--auth-user john@example.org \</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">--auth-password summersun</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="apt install -y libnet-ssleay-perlswaks --server localhost --to john@example.org \ --port 587 -tls \ --auth-user john@example.org \ --auth-password summersun"><div></div></button></div></figure></div>
<aside aria-label="What is Port 465?" class="starlight-aside starlight-aside--tip"> <p class="starlight-aside__title" aria-hidden="true"> <svg aria-hidden="true" class="starlight-aside__icon astro-c6vsoqas" width="16" height="16" viewBox="0 0 24 24" fill="currentColor" style="--sl-icon-size: 1em;"><path fill-rule="evenodd" d="M1.44 8.855v-.001l3.527-3.516c.34-.344.802-.541 1.285-.548h6.649l.947-.947c3.07-3.07 6.207-3.072 7.62-2.868a1.821 1.821 0 0 1 1.557 1.557c.204 1.413.203 4.55-2.868 7.62l-.946.946v6.649a1.845 1.845 0 0 1-.549 1.286l-3.516 3.528a1.844 1.844 0 0 1-3.11-.944l-.858-4.275-4.52-4.52-2.31-.463-1.964-.394A1.847 1.847 0 0 1 .98 10.693a1.843 1.843 0 0 1 .46-1.838Zm5.379 2.017-3.873-.776L6.32 6.733h4.638l-4.14 4.14Zm8.403-5.655c2.459-2.46 4.856-2.463 5.89-2.33.134 1.035.13 3.432-2.329 5.891l-6.71 6.71-3.561-3.56 6.71-6.711Zm-1.318 15.837-.776-3.873 4.14-4.14v4.639l-3.364 3.374Z" clip-rule="evenodd"/><path d="M9.318 18.345a.972.972 0 0 0-1.86-.561c-.482 1.435-1.687 2.204-2.934 2.619a8.22 8.22 0 0 1-1.23.302c.062-.365.157-.79.303-1.229.415-1.247 1.184-2.452 2.62-2.935a.971.971 0 1 0-.62-1.842c-.12.04-.236.084-.35.13-2.02.828-3.012 2.588-3.493 4.033a10.383 10.383 0 0 0-.51 2.845l-.001.016v.063c0 .536.434.972.97.972H2.24a7.21 7.21 0 0 0 .878-.065c.527-.063 1.248-.19 2.02-.447 1.445-.48 3.205-1.472 4.033-3.494a5.828 5.828 0 0 0 .147-.407Z"/></svg>What is Port 465? </p> <div class="starlight-aside__content"> <p>This TCP port belongs to the “submission over TLS” service. It is used for the submission service but expects an encrypted connection from the first byte. This port is hardly ever used so you dont have to care about it. The submission service you just configured is also encrypted but uses the STARTTLS mechanism to switch to a TLS connection after the welcome message.</p> </div> </aside>
<div class="sl-heading-wrapper level-h2"><h2 id="protecting-against-forged-sender-addresses">Protecting against forged sender addresses</h2><a class="sl-anchor-link" href="#protecting-against-forged-sender-addresses"><span aria-hidden="true" class="sl-anchor-icon"><svg width="16" height="16" viewBox="0 0 24 24"><path fill="currentcolor" d="m12.11 15.39-3.88 3.88a2.52 2.52 0 0 1-3.5 0 2.47 2.47 0 0 1 0-3.5l3.88-3.88a1 1 0 0 0-1.42-1.42l-3.88 3.89a4.48 4.48 0 0 0 6.33 6.33l3.89-3.88a1 1 0 1 0-1.42-1.42Zm8.58-12.08a4.49 4.49 0 0 0-6.33 0l-3.89 3.88a1 1 0 0 0 1.42 1.42l3.88-3.88a2.52 2.52 0 0 1 3.5 0 2.47 2.47 0 0 1 0 3.5l-3.88 3.88a1 1 0 1 0 1.42 1.42l3.88-3.89a4.49 4.49 0 0 0 0-6.33ZM8.83 15.17a1 1 0 0 0 1.1.22 1 1 0 0 0 .32-.22l4.92-4.92a1 1 0 0 0-1.42-1.42l-4.92 4.92a1 1 0 0 0 0 1.42Z"></path></svg></span><span class="sr-only">Section titled “Protecting against forged sender addresses”</span></a></div>
<p>A “forged” sender address means that someone claims to be someone else. Lets say that John has authenticated and the mail server trusts him. Nothing keeps John from impersonating someone else and sending email in his name? Most email service providers have restrictions that you can only send emails if the sender matches your actual email address. Lets do that, too.</p>
<p>Postfix provides a setting called <a href="http://www.postfix.org/postconf.5.html#smtpd_sender_login_maps">smtpd_sender_login_maps</a> for that purpose. From the “maps” part you can deduce that it expects a <em>mapping</em> again. This time the two columns mean…</p>
<ul>
<li>Left column: who you claim to be (emails sender address)</li>
<li>Right column: who you logged in as (user name after authentiation)</li>
</ul>
<p>As we use the email address also as a user name we simply need a mapping where the email address is listed on both sides. Fortunately we already have a mapping like that: our <em>email2email</em> mapping that we used earlier as a workaround for catchall forwardings. Lets reuse it. Please run…</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">postconf smtpd_sender_login_maps=mysql:/etc/postfix/mysql-email2email.cf</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="postconf smtpd_sender_login_maps=mysql:/etc/postfix/mysql-email2email.cf"><div></div></button></div></figure></div>
<p>This sets the parameter both for the SMTP port (25) and the submission port (587). Defining these maps is not enough though. You also need to make Postfix act on this. Edit the /etc/postfix/master.cf again and in the <em>submission</em> section add the following option. Make sure the line is indented like all other options:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">-o smtpd_sender_restrictions=reject_sender_login_mismatch,permit_sasl_authenticated,reject</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code=" -o smtpd_sender_restrictions=reject_sender_login_mismatch,permit_sasl_authenticated,reject"><div></div></button></div></figure></div>
<p>Restart Postfix after this change:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">systemctl restart postfix</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="systemctl restart postfix"><div></div></button></div></figure></div>
<p>You can now try to send email as a different user than you are logged in. Lets us swaks again to send a spoofed email:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">swaks --server localhost --from john@example.com \</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">--to john@example.org --port 587 -tls \</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">--auth-user john@example.org \</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">--auth-password summersun</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="swaks --server localhost --from john@example.com \ --to john@example.org --port 587 -tls \ --auth-user john@example.org \ --auth-password summersun"><div></div></button></div></figure></div>
<p>Please note that Johns actual email address is <strong>not</strong> john@example.<strong>com</strong> but john@example.<strong>org</strong>. So it must be rejected. The server should tell you:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">~> MAIL FROM:john@example.com</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">&#x3C;~ 250 2.1.0 Ok</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">~> RCPT TO:john@example.org</span></div></div><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">&#x3C;~ * 553 5.7.1 john@example.com: Sender address rejected: not owned by user john@example.org</span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="~> MAIL FROM:john@example.com<~ 250 2.1.0 Ok~> RCPT TO:john@example.org<~ * 553 5.7.1 john@example.com: Sender address rejected: not owned by user john@example.org"><div></div></button></div></figure></div>
<p>Sorry if the mixture of example.org and example.com in my examples makes this guide less readable. But I cant use any real world domains here. Please just note that sometimes its “.com” and sometimes “.org”.</p>
<p>Of course you can test your new security feature in the Roundcube web mail interface as well. In Settings/Identities you can create another sender email address as in:</p>
<p><img src="/_astro/relaying-roundcube-selecting-identity.DAlNSaQW_kYpJu.webp" alt="Selecting another identity in Roundcube" loading="lazy" decoding="async" fetchpriority="auto" width="440" height="123"></p>
<p>With this wrong sender address any email should get rejected. Your mail.log would read something like:</p>
<div class="expressive-code"><figure class="frame not-content"><figcaption class="header"></figcaption><pre data-language="plaintext"><code><div class="ec-line"><div class="code"><span style="--0:#d6deeb;--1:#403f53">NOQUEUE: reject: RCPT from foo.bar\[…\]:</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">553 5.7.1 &#x3C;someoneelse@example.com>:</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">Sender address rejected:</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">not owned by user john@example.org;</span></div></div><div class="ec-line"><div class="code"><span class="indent"><span style="--0:#d6deeb;--1:#403f53"> </span></span><span style="--0:#d6deeb;--1:#403f53">from=&#x3C;someoneelse@example.com> to=&#x3C;…></span></div></div></code></pre><div class="copy"><div aria-live="polite"></div><button title="Copy to clipboard" data-copied="Copied!" data-code="NOQUEUE: reject: RCPT from foo.bar\[…\]: 553 5.7.1 <someoneelse@example.com>: Sender address rejected: not owned by user john@example.org; from=<someoneelse@example.com> to=<…>"><div></div></button></div></figure></div>
<aside aria-label="Allow aliases?" class="starlight-aside starlight-aside--tip"> <p class="starlight-aside__title" aria-hidden="true"> <svg aria-hidden="true" class="starlight-aside__icon astro-c6vsoqas" width="16" height="16" viewBox="0 0 24 24" fill="currentColor" style="--sl-icon-size: 1em;"><path fill-rule="evenodd" d="M1.44 8.855v-.001l3.527-3.516c.34-.344.802-.541 1.285-.548h6.649l.947-.947c3.07-3.07 6.207-3.072 7.62-2.868a1.821 1.821 0 0 1 1.557 1.557c.204 1.413.203 4.55-2.868 7.62l-.946.946v6.649a1.845 1.845 0 0 1-.549 1.286l-3.516 3.528a1.844 1.844 0 0 1-3.11-.944l-.858-4.275-4.52-4.52-2.31-.463-1.964-.394A1.847 1.847 0 0 1 .98 10.693a1.843 1.843 0 0 1 .46-1.838Zm5.379 2.017-3.873-.776L6.32 6.733h4.638l-4.14 4.14Zm8.403-5.655c2.459-2.46 4.856-2.463 5.89-2.33.134 1.035.13 3.432-2.329 5.891l-6.71 6.71-3.561-3.56 6.71-6.711Zm-1.318 15.837-.776-3.873 4.14-4.14v4.639l-3.364 3.374Z" clip-rule="evenodd"/><path d="M9.318 18.345a.972.972 0 0 0-1.86-.561c-.482 1.435-1.687 2.204-2.934 2.619a8.22 8.22 0 0 1-1.23.302c.062-.365.157-.79.303-1.229.415-1.247 1.184-2.452 2.62-2.935a.971.971 0 1 0-.62-1.842c-.12.04-.236.084-.35.13-2.02.828-3.012 2.588-3.493 4.033a10.383 10.383 0 0 0-.51 2.845l-.001.016v.063c0 .536.434.972.97.972H2.24a7.21 7.21 0 0 0 .878-.065c.527-.063 1.248-.19 2.02-.447 1.445-.48 3.205-1.472 4.033-3.494a5.828 5.828 0 0 0 .147-.407Z"/></svg>Allow aliases? </p> <div class="starlight-aside__content"> <p>If you want to allow users to send as one of their aliases you could create a new *.cf file with a mapping query like this:</p><p><code dir="auto">SELECT email FROM virtual_users WHERE email='%s' UNION SELECT destination FROM virtual_aliases WHERE source='%s'</code></p> </div> </aside> </div> <footer> <footer class="sl-flex astro-3yyafb3n"> <div class="meta sl-flex astro-3yyafb3n"> <p>Last updated: <time datetime="2023-10-04T00:00:00.000Z">Oct 4, 2023</time></p> </div> <div class="pagination-links print:hidden astro-u2l5gyhi" dir="ltr"> <a href="/ispmail-bookworm/testing-email-delivery/" rel="prev" class="astro-u2l5gyhi"> <svg aria-hidden="true" class="astro-u2l5gyhi astro-c6vsoqas" width="16" height="16" viewBox="0 0 24 24" fill="currentColor" style="--sl-icon-size: 1.5rem;"><path d="M17 11H9.41l3.3-3.29a1.004 1.004 0 1 0-1.42-1.42l-5 5a1 1 0 0 0-.21.33 1 1 0 0 0 0 .76 1 1 0 0 0 .21.33l5 5a1.002 1.002 0 0 0 1.639-.325 1 1 0 0 0-.219-1.095L9.41 13H17a1 1 0 0 0 0-2Z"/></svg> <span class="astro-u2l5gyhi"> Previous <br class="astro-u2l5gyhi"> <span class="link-title astro-u2l5gyhi">Testing email delivery</span> </span> </a> <a href="/ispmail-bookworm/catching-spam-with-rspamd/" rel="next" class="astro-u2l5gyhi"> <svg aria-hidden="true" class="astro-u2l5gyhi astro-c6vsoqas" width="16" height="16" viewBox="0 0 24 24" fill="currentColor" style="--sl-icon-size: 1.5rem;"><path d="M17.92 11.62a1.001 1.001 0 0 0-.21-.33l-5-5a1.003 1.003 0 1 0-1.42 1.42l3.3 3.29H7a1 1 0 0 0 0 2h7.59l-3.3 3.29a1.002 1.002 0 0 0 .325 1.639 1 1 0 0 0 1.095-.219l5-5a1 1 0 0 0 .21-.33 1 1 0 0 0 0-.76Z"/></svg> <span class="astro-u2l5gyhi"> Next <br class="astro-u2l5gyhi"> <span class="link-title astro-u2l5gyhi">Catching spam with rspamd</span> </span> </a> </div> </footer> <script defer src="https://comentario.workaround.org/comentario.js"></script>
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