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<a href="https://github.com/docker-mailserver/docker-mailserver/edit/master/docs/content/config/security/ssl.md" title="Edit this page" class="md-content__button md-icon">
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M20.71 7.04c.39-.39.39-1.04 0-1.41l-2.34-2.34c-.37-.39-1.02-.39-1.41 0l-1.84 1.83 3.75 3.75M3 17.25V21h3.75L17.81 9.93l-3.75-3.75L3 17.25z"/></svg>
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<h1>SSL/TLS</h1>
<p>There are multiple options to enable SSL (via <a href="../../environment/#ssl_type"><code>SSL_TYPE</code></a>):</p>
<ul>
<li>Using <a href="#lets-encrypt-recommended">letsencrypt</a> (recommended)</li>
<li>Using <a href="#caddy">Caddy</a></li>
<li>Using <a href="#traefik-v2">Traefik</a></li>
<li>Using <a href="#self-signed-certificates">self-signed certificates</a></li>
<li>Using <a href="#bring-your-own-certificates">your own certificates</a></li>
</ul>
<p>After installation, you can test your setup with:</p>
<ul>
<li><a href="https://www.checktls.com/TestReceiver"><code>checktls.com</code></a></li>
<li><a href="https://github.com/drwetter/testssl.sh"><code>testssl.sh</code></a></li>
</ul>
<div class="admonition warning">
<p class="admonition-title">Exposure of DNS labels through Certificate Transparency</p>
<p>All public Certificate Authorities (CAs) are required to log certificates they issue publicly via <a href="https://certificate.transparency.dev/">Certificate Transparency</a>. This helps to better establish trust.</p>
<p>When using a public CA for certificates used in private networks, be aware that the associated DNS labels in the certificate are logged publicly and <a href="https://crt.sh/">easily searchable</a>. These logs are <em>append only</em>, you <strong>cannot</strong> redact this information.</p>
<p>You could use a <a href="https://en.wikipedia.org/wiki/Wildcard_certificate#Examples">wildcard certificate</a>. This avoids accidentally leaking information to the internet, but keep in mind the <a href="https://gist.github.com/joepie91/7e5cad8c0726fd6a5e90360a754fc568">potential security risks</a> of wildcard certs.</p>
</div>
<h2 id="lets-encrypt-recommended"><a class="toclink" href="#lets-encrypt-recommended">Let's Encrypt (Recommended)</a></h2>
<p>To enable <em>Let's Encrypt</em> for <code>docker-mailserver</code>, you have to:</p>
<ol>
<li>Get your certificate using the <em>Let's Encrypt</em> client <a href="https://github.com/certbot/certbot">Certbot</a>.</li>
<li>
<p>For your <code>docker-mailserver</code> container:</p>
<ol>
<li>Add the environment variable <code>SSL_TYPE=letsencrypt</code>.</li>
<li>Mount <a href="https://certbot.eff.org/docs/using.html#where-are-my-certificates">your local <code>letsencrypt</code> folder</a> as a volume to <code>/etc/letsencrypt</code>.</li>
</ol>
</li>
</ol>
<p>You don't have to do anything else. Enjoy!</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p><code>/etc/letsencrypt/live</code> stores provisioned certificates in individual folders named by their FQDN (<em>Fully Qualified Domain Name</em>). <code>docker-mailserver</code> looks for it's certificate folder via the <code>hostname</code> command. The FQDN inside the docker container is derived from the <code>--hostname</code> and <code>--domainname</code> options.</p>
</div>
<div class="admonition example">
<p class="admonition-title">Example</p>
<p>Add these additions to the <code>mailserver</code> service in your <a href="https://github.com/docker-mailserver/docker-mailserver/blob/master/docker-compose.yml"><code>docker-compose.yml</code></a>:</p>
<div class="highlight"><pre><span></span><code><span class="nt">services</span><span class="p">:</span>
<span class="nt">mailserver</span><span class="p">:</span>
<span class="c1"># For the FQDN &#39;mail.example.com&#39;:</span>
<span class="nt">hostname</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">mail</span>
<span class="nt">domainname</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">example.com</span>
<span class="nt">environment</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">SSL_TYPE=letsencrypt</span>
<span class="nt">volumes</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">/etc/letsencrypt:/etc/letsencrypt</span>
</code></pre></div>
</div>
<h3 id="example-using-docker-for-lets-encrypt"><a class="toclink" href="#example-using-docker-for-lets-encrypt">Example using Docker for <em>Let's Encrypt</em></a></h3>
<ul>
<li>Certbot provisions certificates to <code>/etc/letsencrypt</code>. Add a volume to store these, so that they can later be accessed by <code>docker-mailserver</code> container.</li>
<li>
<p>You may also want to persist Certbot <a href="https://certbot.eff.org/docs/using.html#log-rotation">logs</a>, just in case you need to troubleshoot.</p>
</li>
<li>
<p>Getting a certificate is this simple! (<em>Referencing: <a href="https://certbot.eff.org/docs/install.html#running-with-docker">Certbot docker instructions</a> and <a href="https://certbot.eff.org/docs/using.html#standalone"><code>certonly --standalone</code> mode</a></em>):</p>
<div class="highlight"><pre><span></span><code><span class="c1"># Change `mail.example.com` below to your own FQDN.</span>
<span class="c1"># Requires access to port 80 from the internet, adjust your firewall if needed.</span>
docker run --rm -it <span class="se">\</span>
-v <span class="s2">&quot;</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">/docker-data/certbot/certs/:/etc/letsencrypt/&quot;</span> <span class="se">\</span>
-v <span class="s2">&quot;</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">/docker-data/certbot/logs/:/var/log/letsencrypt/&quot;</span> <span class="se">\</span>
-p <span class="m">80</span>:80 <span class="se">\</span>
certbot/certbot certonly --standalone -d mail.example.com
</code></pre></div>
</li>
<li>
<p>Add a volume for <code>docker-mailserver</code> that maps the <em>local <code>certbot/certs/</code> folder</em> to the container path <code>/etc/letsencrypt/</code>.</p>
</li>
<li>The certificate setup is complete, but remember <em>it will expire</em>. Consider automating renewals.</li>
</ul>
<div class="admonition tip">
<p class="admonition-title">Renewing Certificates</p>
<p>When running the above <code>certonly --standalone</code> snippet again, the existing certificate is renewed if it would expire within 30 days.</p>
<p>Alternatively, Certbot can look at all the certificates it manages, and only renew those nearing their expiry via the <a href="https://certbot.eff.org/docs/using.html#renewing-certificates"><code>renew</code> command</a>:</p>
<div class="highlight"><pre><span></span><code><span class="c1"># This will need access to port 443 from the internet, adjust your firewall if needed.</span>
docker run --rm -it <span class="se">\</span>
-v <span class="s2">&quot;</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">/docker-data/certbot/certs/:/etc/letsencrypt/&quot;</span> <span class="se">\</span>
-v <span class="s2">&quot;</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">/docker-data/certbot/logs/:/var/log/letsencrypt/&quot;</span> <span class="se">\</span>
-p <span class="m">80</span>:80 <span class="se">\</span>
-p <span class="m">443</span>:443 <span class="se">\</span>
certbot/certbot renew
</code></pre></div>
<p>This process can also be <a href="https://certbot.eff.org/docs/using.html#automated-renewals">automated via <em>cron</em> or <em>systemd timers</em></a>.</p>
</div>
<div class="admonition note">
<p class="admonition-title">Using a different ACME CA</p>
<p>Certbot does support <a href="https://certbot.eff.org/docs/using.htmlchanging-the-acme-server">alternative certificate providers via the <code>--server</code></a> option. In most cases you'll want to use the default <em>Let's Encrypt</em>.</p>
</div>
<h3 id="example-using-nginx-proxy-and-acme-companion-with-docker"><a class="toclink" href="#example-using-nginx-proxy-and-acme-companion-with-docker">Example using <code>nginx-proxy</code> and <code>acme-companion</code> with Docker</a></h3>
<p>If you are running a web server already, port 80 will be in use which Certbot requires. You could use the <a href="https://certbot.eff.org/docs/using.html#webroot">Certbot <code>--webroot</code></a> feature, but it is more common to leverage a <em>reverse proxy</em> that manages the provisioning and renewal of certificates for your services automatically.</p>
<p>In the following example, we show how <code>docker-mailserver</code> can be run alongside the docker containers <a href="https://github.com/nginx-proxy/nginx-proxy"><code>nginx-proxy</code></a> and <a href="https://github.com/nginx-proxy/acme-companion"><code>acme-companion</code></a> (<em>Referencing: <a href="https://github.com/nginx-proxy/acme-companion/blob/main/docs"><code>acme-companion</code> documentation</a></em>):</p>
<ol>
<li>
<p>Start the <em>reverse proxy</em> (<code>nginx-proxy</code>):</p>
<div class="highlight"><pre><span></span><code>docker run --detach <span class="se">\</span>
--name nginx-proxy <span class="se">\</span>
--restart always <span class="se">\</span>
--publish <span class="m">80</span>:80 <span class="se">\</span>
--publish <span class="m">443</span>:443 <span class="se">\</span>
--volume <span class="s2">&quot;</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">/docker-data/nginx-proxy/html/:/usr/share/nginx/html/&quot;</span> <span class="se">\</span>
--volume <span class="s2">&quot;</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">/docker-data/nginx-proxy/vhost.d/:/etc/nginx/vhost.d/&quot;</span> <span class="se">\</span>
--volume <span class="s2">&quot;</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">/docker-data/acme-companion/certs/:/etc/nginx/certs/:ro&quot;</span> <span class="se">\</span>
--volume <span class="s1">&#39;/var/run/docker.sock:/tmp/docker.sock:ro&#39;</span> <span class="se">\</span>
nginxproxy/nginx-proxy
</code></pre></div>
</li>
<li>
<p>Then start the <em>certificate provisioner</em> (<code>acme-companion</code>), which will provide certificates to <code>nginx-proxy</code>:</p>
<div class="highlight"><pre><span></span><code><span class="c1"># Inherit `nginx-proxy` volumes via `--volumes-from`, but make `certs/` writeable:</span>
docker run --detach <span class="se">\</span>
--name nginx-proxy-acme <span class="se">\</span>
--restart always <span class="se">\</span>
--volumes-from nginx-proxy <span class="se">\</span>
--volume <span class="s2">&quot;</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">/docker-data/acme-companion/certs/:/etc/nginx/certs/:rw&quot;</span> <span class="se">\</span>
--volume <span class="s2">&quot;</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">/docker-data/acme-companion/acme-state/:/etc/acme.sh/&quot;</span> <span class="se">\</span>
--volume <span class="s1">&#39;/var/run/docker.sock:/var/run/docker.sock:ro&#39;</span> <span class="se">\</span>
--env <span class="s1">&#39;DEFAULT_EMAIL=admin@example.com&#39;</span> <span class="se">\</span>
nginxproxy/acme-companion
</code></pre></div>
</li>
<li>
<p>Start the rest of your web server containers as usual.</p>
</li>
<li>
<p>Start a <em>dummy container</em> to provision certificatess for your FQDN (eg: <code>mail.example.com</code>). <code>acme-companion</code> will detect the container and generate a <em>Let's Encrypt</em> certificate for your domain, which can be used by <code>docker-mailserver</code>:</p>
<div class="highlight"><pre><span></span><code>docker run --detach <span class="se">\</span>
--name webmail <span class="se">\</span>
--env <span class="s1">&#39;VIRTUAL_HOST=mail.example.com&#39;</span> <span class="se">\</span>
--env <span class="s1">&#39;LETSENCRYPT_HOST=mail.example.com&#39;</span> <span class="se">\</span>
--env <span class="s1">&#39;LETSENCRYPT_EMAIL=admin@example.com&#39;</span> <span class="se">\</span>
nginx
</code></pre></div>
<p>You may want to add <code>--env LETSENCRYPT_TEST=true</code> to the above while testing, to avoid the <em>Let's Encrypt</em> certificate generation rate limits.</p>
</li>
<li>
<p>Make sure your mount path to the <code>letsencrypt</code> certificates directory is correct. Edit your <code>docker-compose.yml</code> for the <code>mailserver</code> service to have volumes added like below:</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">./docker-data/dms/mail-data/:/var/mail/</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/dms/mail-state/:/var/mail-state/</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/dms/config/:/tmp/docker-mailserver/</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/acme-companion/certs/:/etc/letsencrypt/live/:ro</span>
</code></pre></div>
</li>
<li>
<p>Then from the <code>docker-compose.yml</code> project directory, run: <code>docker-compose up -d mailserver</code>.</p>
</li>
</ol>
<h3 id="example-using-nginx-proxy-and-acme-companion-with-docker-compose"><a class="toclink" href="#example-using-nginx-proxy-and-acme-companion-with-docker-compose">Example using <code>nginx-proxy</code> and <code>acme-companion</code> with <code>docker-compose</code></a></h3>
<p>The following example is the <a href="https://github.com/nginx-proxy/acme-companion#basic-usage-with-the-nginx-proxy-container">basic setup</a> you need for using <code>nginx-proxy</code> and <code>acme-companion</code> with <code>docker-mailserver</code> (<em>Referencing: <a href="https://github.com/nginx-proxy/acme-companion/blob/main/docs"><code>acme-companion</code> documentation</a></em>):</p>
<details class="example" open="open"><summary>Example: <code>docker-compose.yml</code></summary><p>You should have an existing <code>docker-compose.yml</code> with a <code>mailserver</code> service. Below are the modifications to add for integrating with <code>nginx-proxy</code> and <code>acme-companion</code> services:</p>
<div class="highlight"><pre><span></span><code><span class="nt">version</span><span class="p">:</span> <span class="s">&#39;3.8&#39;</span>
<span class="nt">services</span><span class="p">:</span>
<span class="c1"># Add the following `environment` and `volumes` to your existing `mailserver` service:</span>
<span class="nt">mailserver</span><span class="p">:</span>
<span class="nt">environment</span><span class="p">:</span>
<span class="c1"># SSL_TYPE: Uses the `letsencrypt` method to find mounted certificates.</span>
<span class="c1"># VIRTUAL_HOST: The FQDN that `nginx-proxy` will configure itself to handle for HTTP[S] connections.</span>
<span class="c1"># LETSENCRYPT_HOST: The FQDN for a certificate that `acme-companion` will provision and renew.</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">SSL_TYPE=letsencrypt</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">VIRTUAL_HOST=mail.example.com</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">LETSENCRYPT_HOST=mail.example.com</span>
<span class="nt">volumes</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/acme-companion/certs/:/etc/letsencrypt/live/:ro</span>
<span class="c1"># If you don&#39;t yet have your own `nginx-proxy` and `acme-companion` setup,</span>
<span class="c1"># here is an example you can use:</span>
<span class="nt">reverse-proxy</span><span class="p">:</span>
<span class="nt">image</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">nginxproxy/nginx-proxy</span>
<span class="nt">container_name</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">nginx-proxy</span>
<span class="nt">restart</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">always</span>
<span class="nt">ports</span><span class="p">:</span>
<span class="c1"># Port 80: Required for HTTP-01 challenges to `acme-companion`.</span>
<span class="c1"># Port 443: Only required for containers that need access over HTTPS. TLS-ALPN-01 challenge not supported.</span>
<span class="p p-Indicator">-</span> <span class="s">&quot;80:80&quot;</span>
<span class="p p-Indicator">-</span> <span class="s">&quot;443:443&quot;</span>
<span class="nt">volumes</span><span class="p">:</span>
<span class="c1"># `certs/`: Managed by the `acme-companion` container (_read-only_).</span>
<span class="c1"># `docker.sock`: Required to interact with containers via the Docker API.</span>
<span class="c1"># `dhparam`: A named data volume to prevent `nginx-proxy` creating an anonymous volume each time.</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/nginx-proxy/html/:/usr/share/nginx/html/</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/nginx-proxy/vhost.d/:/etc/nginx/vhost.d/</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/acme-companion/certs/:/etc/nginx/certs/:ro</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">/var/run/docker.sock:/tmp/docker.sock:ro</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">dhparam:/etc/nginx/dhparam</span>
<span class="nt">acme-companion</span><span class="p">:</span>
<span class="nt">image</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">nginxproxy/acme-companion</span>
<span class="nt">container_name</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">nginx-proxy-acme</span>
<span class="nt">restart</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">always</span>
<span class="nt">environment</span><span class="p">:</span>
<span class="c1"># Only docker-compose v2 supports: `volumes_from: [nginx-proxy]`,</span>
<span class="c1"># reference the _reverse-proxy_ `container_name` here:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">NGINX_PROXY_CONTAINER=nginx-proxy</span>
<span class="nt">volumes</span><span class="p">:</span>
<span class="c1"># `html/`: Write ACME HTTP-01 challenge files that `nginx-proxy` will serve.</span>
<span class="c1"># `vhost.d/`: To enable web access via `nginx-proxy` to HTTP-01 challenge files.</span>
<span class="c1"># `certs/`: To store certificates and private keys.</span>
<span class="c1"># `acme-state/`: To persist config and state for the ACME provisioner (`acme.sh`).</span>
<span class="c1"># `docker.sock`: Required to interact with containers via the Docker API.</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/nginx-proxy/html/:/usr/share/nginx/html/</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/nginx-proxy/vhost.d/:/etc/nginx/vhost.d/</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/acme-companion/certs/:/etc/nginx/certs/:rw</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/acme-companion/acme-state/:/etc/acme.sh/</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">/var/run/docker.sock:/var/run/docker.sock:ro</span>
<span class="c1"># Once `nginx-proxy` fixes their Dockerfile, this named data volume can be removed from docs.</span>
<span class="c1"># Users can opt for a local bind mount volume like all others if they prefer, but this volume</span>
<span class="c1"># is only intended to be temporary.</span>
<span class="nt">volumes</span><span class="p">:</span>
<span class="nt">dhparam</span><span class="p">:</span>
</code></pre></div>
</details>
<div class="admonition tip">
<p class="admonition-title">Optional ENV vars worth knowing about</p>
<p><a href="https://github.com/nginx-proxy/acme-companion/blob/main/docs/Let's-Encrypt-and-ACME.md">Per container ENV</a> that <code>acme-companion</code> will detect to override default provisioning settings:</p>
<ul>
<li><code>LETSENCRYPT_TEST=true</code>: <em>Recommended during initial setup</em>. Otherwise the default production endpoint has a <a href="https://letsencrypt.org/docs/rate-limits/">rate limit of 5 duplicate certificates per week</a>. Overrides <code>ACME_CA_URI</code> to use the <em>Let's Encrypt</em> staging endpoint.</li>
<li><code>LETSENCRYPT_EMAIL</code>: For when you don't use <code>DEFAULT_EMAIL</code> on <code>acme-companion</code>, or want to assign a different email contact for this container.</li>
<li><code>LETSENCRYPT_KEYSIZE</code>: Allows you to configure the type (RSA or ECDSA) and size of the private key for your certificate. Default is RSA 4096.</li>
<li><code>LETSENCRYPT_RESTART_CONTAINER=true</code>: When the certificate is renewed, the entire container will be restarted to ensure the new certificate is used.</li>
</ul>
<p><a href="https://github.com/nginx-proxy/acme-companion/blob/main/docs/Container-configuration.md"><code>acme-companion</code> ENV for default settings</a> that apply to all containers using <code>LETSENCRYPT_HOST</code>:</p>
<ul>
<li><code>DEFAULT_EMAIL</code>: An email address that the CA (<em>eg: Let's Encrypt</em>) can contact you about expiring certificates, failed renewals, or for account recovery. You may want to use an email address not handled by your mail-server to ensure deliverability in the event your mail-server breaks.</li>
<li><code>CERTS_UPDATE_INTERVAL</code>: If you need to adjust the frequency to check for renewals. 3600 seconds (1 hour) by default.</li>
<li><code>DEBUG=1</code>: Should be helpful when <a href="https://github.com/nginx-proxy/acme-companion/blob/main/docs/Invalid-authorizations.md">troubleshooting provisioning issues</a> from <code>acme-companion</code> logs.</li>
<li><code>ACME_CA_URI</code>: Useful in combination with <code>CA_BUNDLE</code> to use a private CA. To change the default <em>Let's Encrypt</em> endpoint to the staging endpoint, use <code>https://acme-staging-v02.api.letsencrypt.org/directory</code>.</li>
<li><code>CA_BUNDLE</code>: If you want to use a private CA instead of <em>Let's Encrypt</em>.</li>
</ul>
</div>
<div class="admonition tip">
<p class="admonition-title">Alternative to required ENV on <code>mailserver</code> service</p>
<p>While you will still need both <code>nginx-proxy</code> and <code>acme-companion</code> containers, you can manage certificates without adding ENV vars to containers. Instead the ENV is moved into a file and uses the <code>acme-companion</code> feature <a href="https://github.com/nginx-proxy/acme-companion/blob/main/docs/Standalone-certificates.md">Standalone certificates</a>.</p>
<p>This requires adding another shared volume between <code>nginx-proxy</code> and <code>acme-companion</code>:</p>
<div class="highlight"><pre><span></span><code><span class="nt">services</span><span class="p">:</span>
<span class="nt">reverse-proxy</span><span class="p">:</span>
<span class="nt">volumes</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/nginx-proxy/conf.d/:/etc/nginx/conf.d/</span>
<span class="nt">acme-companion</span><span class="p">:</span>
<span class="nt">volumes</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/nginx-proxy/conf.d/:/etc/nginx/conf.d/</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/acme-companion/standalone.sh:/app/letsencrypt_user_data:ro</span>
</code></pre></div>
<p><code>acme-companion</code> mounts a shell script (<code>standalone.sh</code>), which defines variables to customize certificate provisioning:</p>
<div class="highlight"><pre><span></span><code><span class="c1"># A list IDs for certificates to provision:</span>
<span class="nv">LETSENCRYPT_STANDALONE_CERTS</span><span class="o">=(</span><span class="s1">&#39;mail&#39;</span><span class="o">)</span>
<span class="c1"># Each ID inserts itself into the standard `acme-companion` supported container ENV vars below.</span>
<span class="c1"># The LETSENCRYPT_&lt;ID&gt;_HOST var is a list of FQDNs to provision a certificate for as the SAN field:</span>
<span class="nv">LETSENCRYPT_mail_HOST</span><span class="o">=(</span><span class="s1">&#39;mail.example.com&#39;</span><span class="o">)</span>
<span class="c1"># Optional variables:</span>
<span class="nv">LETSENCRYPT_mail_TEST</span><span class="o">=</span><span class="nb">true</span>
<span class="nv">LETSENCRYPT_mail_EMAIL</span><span class="o">=</span><span class="s1">&#39;admin@example.com&#39;</span>
<span class="c1"># RSA-4096 =&gt; `4096`, ECDSA-256 =&gt; `ec-256`:</span>
<span class="nv">LETSENCRYPT_mail_KEYSIZE</span><span class="o">=</span><span class="m">4096</span>
</code></pre></div>
<p>Unlike with the equivalent ENV for containers, <a href="https://github.com/nginx-proxy/acme-companion/blob/main/docs/Standalone-certificates.md#picking-up-changes-to-letsencrypt_user_data">changes to this file will <strong>not</strong> be detected automatically</a>. You would need to wait until the next renewal check by <code>acme-companion</code> (<em>every hour by default</em>), restart <code>acme-companion</code>, or <a href="https://github.com/nginx-proxy/acme-companion/blob/main/docs/Container-utilities.md">manually invoke the <em>service loop</em></a>:</p>
<p><code class="highlight">docker <span class="nb">exec</span> nginx-proxy-acme /app/signal_le_service</code></p>
</div>
<h3 id="example-using-lets-encrypt-certificates-with-a-synology-nas"><a class="toclink" href="#example-using-lets-encrypt-certificates-with-a-synology-nas">Example using <em>Let's Encrypt</em> Certificates with a <em>Synology NAS</em></a></h3>
<p>Version 6.2 and later of the Synology NAS DSM OS now come with an interface to generate and renew letencrypt certificates. Navigation into your DSM control panel and go to Security, then click on the tab Certificate to generate and manage letsencrypt certificates.</p>
<p>Amongst other things, you can use these to secure your mail-server. DSM locates the generated certificates in a folder below <code>/usr/syno/etc/certificate/_archive/</code>.</p>
<p>Navigate to that folder and note the 6 character random folder name of the certificate you'd like to use. Then, add the following to your <code>docker-compose.yml</code> declaration file:</p>
<div class="highlight"><pre><span></span><code><span class="c1"># Note: If you have an existing setup that was working pre docker-mailserver v10.2,</span>
<span class="c1"># &#39;/tmp/dms/custom-certs&#39; below has replaced the previous &#39;/tmp/ssl&#39; container path.</span>
<span class="nt">volumes</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">/usr/syno/etc/certificate/_archive/&lt;your-folder&gt;/:/tmp/dms/custom-certs/</span>
<span class="nt">environment</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">SSL_TYPE=manual</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">SSL_CERT_PATH=/tmp/dms/custom-certs/fullchain.pem</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">SSL_KEY_PATH=/tmp/dms/custom-certs/privkey.pem</span>
</code></pre></div>
<p>DSM-generated letsencrypt certificates get auto-renewed every three months.</p>
<h2 id="caddy"><a class="toclink" href="#caddy">Caddy</a></h2>
<p>If you are using Caddy to renew your certificates, please note that only RSA certificates work. Read <a href="https://github.com/docker-mailserver/docker-mailserver/issues/1440">#1440</a> for details. In short for Caddy v1 the <code>Caddyfile</code> should look something like:</p>
<div class="highlight"><pre><span></span><code>https://mail.example.com {
tls admin@example.com {
key_type rsa2048
}
}
</code></pre></div>
<p>For Caddy v2 you can specify the <code>key_type</code> in your server's global settings, which would end up looking something like this if you're using a <code>Caddyfile</code>:</p>
<div class="highlight"><pre><span></span><code>{
debug
admin localhost:2019
http_port 80
https_port 443
default_sni example.com
key_type rsa4096
}
</code></pre></div>
<p>If you are instead using a json config for Caddy v2, you can set it in your site's TLS automation policies:</p>
<details class="example" open="open"><summary>Example Code</summary><div class="highlight"><pre><span></span><code><span class="p">{</span>
<span class="nt">&quot;apps&quot;</span><span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;http&quot;</span><span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;servers&quot;</span><span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;srv0&quot;</span><span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;listen&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="s2">&quot;:443&quot;</span>
<span class="p">],</span>
<span class="nt">&quot;routes&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="p">{</span>
<span class="nt">&quot;match&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="p">{</span>
<span class="nt">&quot;host&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="s2">&quot;mail.example.com&quot;</span><span class="p">,</span>
<span class="p">]</span>
<span class="p">}</span>
<span class="p">],</span>
<span class="nt">&quot;handle&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="p">{</span>
<span class="nt">&quot;handler&quot;</span><span class="p">:</span> <span class="s2">&quot;subroute&quot;</span><span class="p">,</span>
<span class="nt">&quot;routes&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="p">{</span>
<span class="nt">&quot;handle&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="p">{</span>
<span class="nt">&quot;body&quot;</span><span class="p">:</span> <span class="s2">&quot;&quot;</span><span class="p">,</span>
<span class="nt">&quot;handler&quot;</span><span class="p">:</span> <span class="s2">&quot;static_response&quot;</span>
<span class="p">}</span>
<span class="p">]</span>
<span class="p">}</span>
<span class="p">]</span>
<span class="p">}</span>
<span class="p">],</span>
<span class="nt">&quot;terminal&quot;</span><span class="p">:</span> <span class="kc">true</span>
<span class="p">},</span>
<span class="p">]</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">},</span>
<span class="nt">&quot;tls&quot;</span><span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;automation&quot;</span><span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;policies&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="p">{</span>
<span class="nt">&quot;subjects&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="s2">&quot;mail.example.com&quot;</span><span class="p">,</span>
<span class="p">],</span>
<span class="nt">&quot;key_type&quot;</span><span class="p">:</span> <span class="s2">&quot;rsa2048&quot;</span><span class="p">,</span>
<span class="nt">&quot;issuer&quot;</span><span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;email&quot;</span><span class="p">:</span> <span class="s2">&quot;admin@example.com&quot;</span><span class="p">,</span>
<span class="nt">&quot;module&quot;</span><span class="p">:</span> <span class="s2">&quot;acme&quot;</span>
<span class="p">}</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;issuer&quot;</span><span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;email&quot;</span><span class="p">:</span> <span class="s2">&quot;admin@example.com&quot;</span><span class="p">,</span>
<span class="nt">&quot;module&quot;</span><span class="p">:</span> <span class="s2">&quot;acme&quot;</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">]</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">}</span>
</code></pre></div>
</details>
<p>The generated certificates can be mounted:</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">${CADDY_DATA_DIR}/certificates/acme-v02.api.letsencrypt.org-directory/mail.example.com/mail.example.com.crt:/etc/letsencrypt/live/mail.example.com/fullchain.pem</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">${CADDY_DATA_DIR}/certificates/acme-v02.api.letsencrypt.org-directory/mail.example.com/mail.example.com.key:/etc/letsencrypt/live/mail.example.com/privkey.pem</span>
</code></pre></div>
<p>EC certificates fail in the TLS handshake:</p>
<div class="highlight"><pre><span></span><code><span class="go">CONNECTED(00000003)</span>
<span class="go">140342221178112:error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure:ssl/record/rec_layer_s3.c:1543:SSL alert number 40</span>
<span class="go">no peer certificate available</span>
<span class="go">No client certificate CA names sent</span>
</code></pre></div>
<h2 id="traefik-v2"><a class="toclink" href="#traefik-v2">Traefik v2</a></h2>
<p><a href="https://github.com/containous/traefik">Traefik</a> is an open-source application proxy using the <a href="https://datatracker.ietf.org/doc/html/rfc8555">ACME protocol</a>. <a href="https://github.com/containous/traefik">Traefik</a> can request certificates for domains and subdomains, and it will take care of renewals, challenge negotiations, etc. We strongly recommend to use <a href="https://github.com/containous/traefik">Traefik</a>'s major version 2.</p>
<p><a href="https://github.com/containous/traefik">Traefik</a>'s storage format is natively supported if the <code>acme.json</code> store is mounted into the container at <code>/etc/letsencrypt/acme.json</code>. The file is also monitored for changes and will trigger a reload of the mail services (Postfix and Dovecot). Wild card certificates issued for <code>*.example.com</code> are supported. You will then want to use <code class="highlight"><span class="nv">SSL_DOMAIN</span><span class="o">=</span>example.com</code>. Lookup of the certificate domain happens in the following order:</p>
<ol>
<li><code class="highlight"><span class="si">${</span><span class="nv">SSL_DOMAIN</span><span class="si">}</span></code></li>
<li><code class="highlight"><span class="si">${</span><span class="nv">HOSTNAME</span><span class="si">}</span></code></li>
<li><code class="highlight"><span class="si">${</span><span class="nv">DOMAINNAME</span><span class="si">}</span></code></li>
</ol>
<p>This setup only comes with one caveat: The domain has to be configured on another service for <a href="https://github.com/containous/traefik">Traefik</a> to actually request it from Let'sEncrypt, i.e. <a href="https://github.com/containous/traefik">Traefik</a> will not issue a certificate without a service / router demanding it.</p>
<details class="example" open="open"><summary>Example Code</summary><p>Here is an example setup for <a href="https://docs.docker.com/compose/"><code>docker-compose</code></a>:</p>
<div class="highlight"><pre><span></span><code><span class="nt">version</span><span class="p">:</span> <span class="s">&#39;3.8&#39;</span>
<span class="nt">services</span><span class="p">:</span>
<span class="nt">mailserver</span><span class="p">:</span>
<span class="nt">image</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">docker.io/mailserver/docker-mailserver:latest</span>
<span class="nt">container_name</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">mailserver</span>
<span class="nt">hostname</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">mail</span>
<span class="nt">domainname</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">example.com</span>
<span class="nt">volumes</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/traefik/acme.json:/etc/letsencrypt/acme.json:ro</span>
<span class="nt">environment</span><span class="p">:</span>
<span class="nt">SSL_TYPE</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">letsencrypt</span>
<span class="nt">SSL_DOMAIN</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">mail.example.com</span>
<span class="c1"># for a wildcard certificate, use</span>
<span class="c1"># SSL_DOMAIN: example.com</span>
<span class="nt">reverse-proxy</span><span class="p">:</span>
<span class="nt">image</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">docker.io/traefik:latest</span> <span class="c1">#v2.5</span>
<span class="nt">container_name</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">docker-traefik</span>
<span class="nt">ports</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="s">&quot;80:80&quot;</span>
<span class="p p-Indicator">-</span> <span class="s">&quot;443:443&quot;</span>
<span class="nt">command</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">--providers.docker</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">--entrypoints.http.address=:80</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">--entrypoints.http.http.redirections.entryPoint.to=https</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">--entrypoints.http.http.redirections.entryPoint.scheme=https</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">--entrypoints.https.address=:443</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">--entrypoints.https.http.tls.certResolver=letsencrypt</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">--certificatesresolvers.letsencrypt.acme.email=admin@example.com</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">--certificatesresolvers.letsencrypt.acme.storage=/acme.json</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">--certificatesresolvers.letsencrypt.acme.httpchallenge.entrypoint=http</span>
<span class="nt">volumes</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">./docker-data/traefik/acme.json:/acme.json</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">/var/run/docker.sock:/var/run/docker.sock:ro</span>
<span class="nt">whoami</span><span class="p">:</span>
<span class="nt">image</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain">docker.io/traefik/whoami:latest</span>
<span class="nt">labels</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="s">&quot;traefik.http.routers.whoami.rule=Host(`mail.example.com`)&quot;</span>
</code></pre></div>
</details>
<h2 id="self-signed-certificates"><a class="toclink" href="#self-signed-certificates">Self-Signed Certificates</a></h2>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>Use self-signed certificates only for testing purposes!</p>
</div>
<p>This feature requires you to provide the following files into your <a href="../../advanced/optional-config/"><code>docker-data/dms/config/ssl/</code> directory</a> (<em>internal location: <code>/tmp/docker-mailserver/ssl/</code></em>):</p>
<ul>
<li><code>&lt;FQDN&gt;-key.pem</code></li>
<li><code>&lt;FQDN&gt;-cert.pem</code></li>
<li><code>demoCA/cacert.pem</code></li>
</ul>
<p>Where <code>&lt;FQDN&gt;</code> is the <a href="https://en.wikipedia.org/wiki/Fully_qualified_domain_name">FQDN</a> assigned to <code>docker-mailserver</code> (<em>eg: <code>mail.example.com</code> (FQDN) =&gt; <code>mail</code> (hostname) + <code>example.com</code> (domainname)</em>) via <code>docker run</code> command or <code>docker-compose.yml</code> config.</p>
<p>Add <code>SSL_TYPE=self-signed</code> to your <code>docker-mailserver</code> environment variables. Postfix and Dovecot will be configured to use the provided certificate (<em><code>.pem</code> files above</em>) during container startup.</p>
<h3 id="generating-a-self-signed-certificate"><a class="toclink" href="#generating-a-self-signed-certificate">Generating a self-signed certificate</a></h3>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Since <code>docker-mailserver</code> v10, support in <code>setup.sh</code> for generating a <em>self-signed SSL certificate</em> internally was removed.</p>
</div>
<p>One way to generate self-signed certificates is with <a href="https://smallstep.com/docs/step-cli">Smallstep's <code>step</code> CLI</a>. This is exactly what <a href="https://github.com/docker-mailserver/docker-mailserver/blob/3b8059f2daca80d967635e04d8d81e9abb755a4d/test/test-files/ssl/example.test/README.md"><code>docker-mailserver</code> does for creating test certificates</a>.</p>
<p>For example with the FQDN <code>mail.example.test</code>, you can generate the required files by running:</p>
<div class="highlight"><pre><span></span><code><span class="ch">#! /bin/sh</span>
mkdir -p demoCA
step certificate create <span class="s2">&quot;Smallstep Root CA&quot;</span> <span class="s2">&quot;demoCA/cacert.pem&quot;</span> <span class="s2">&quot;demoCA/cakey.pem&quot;</span> <span class="se">\</span>
--no-password --insecure <span class="se">\</span>
--profile root-ca <span class="se">\</span>
--not-before <span class="s2">&quot;2021-01-01T00:00:00+00:00&quot;</span> <span class="se">\</span>
--not-after <span class="s2">&quot;2031-01-01T00:00:00+00:00&quot;</span> <span class="se">\</span>
--san <span class="s2">&quot;example.test&quot;</span> <span class="se">\</span>
--san <span class="s2">&quot;mail.example.test&quot;</span> <span class="se">\</span>
--kty RSA --size <span class="m">2048</span>
step certificate create <span class="s2">&quot;Smallstep Leaf&quot;</span> mail.example.test-cert.pem mail.example.test-key.pem <span class="se">\</span>
--no-password --insecure <span class="se">\</span>
--profile leaf <span class="se">\</span>
--ca <span class="s2">&quot;demoCA/cacert.pem&quot;</span> <span class="se">\</span>
--ca-key <span class="s2">&quot;demoCA/cakey.pem&quot;</span> <span class="se">\</span>
--not-before <span class="s2">&quot;2021-01-01T00:00:00+00:00&quot;</span> <span class="se">\</span>
--not-after <span class="s2">&quot;2031-01-01T00:00:00+00:00&quot;</span> <span class="se">\</span>
--san <span class="s2">&quot;example.test&quot;</span> <span class="se">\</span>
--san <span class="s2">&quot;mail.example.test&quot;</span> <span class="se">\</span>
--kty RSA --size <span class="m">2048</span>
</code></pre></div>
<p>If you'd rather not install the CLI tool locally to run the <code>step</code> commands above; you can save the script above to a file such as <code>generate-certs.sh</code> (<em>and make it executable <code>chmod +x generate-certs.sh</code></em>) in a directory that you want the certs to be placed (eg: <code>docker-data/dms/custom-certs/</code>), then use docker to run that script in a container:</p>
<div class="highlight"><pre><span></span><code><span class="c1"># &#39;--user&#39; is to keep ownership of the files written to</span>
<span class="c1"># the local volume to use your systems User and Group ID values.</span>
docker run --rm -it <span class="se">\</span>
--user <span class="s2">&quot;</span><span class="k">$(</span>id -u<span class="k">)</span><span class="s2">:</span><span class="k">$(</span>id -g<span class="k">)</span><span class="s2">&quot;</span> <span class="se">\</span>
--volume <span class="s2">&quot;</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">/docker-data/dms/custom-certs/:/tmp/step-ca/&quot;</span> <span class="se">\</span>
--workdir <span class="s2">&quot;/tmp/step-ca/&quot;</span> <span class="se">\</span>
--entrypoint <span class="s2">&quot;/tmp/step-ca/generate-certs.sh&quot;</span> <span class="se">\</span>
smallstep/step-ca
</code></pre></div>
<h2 id="bring-your-own-certificates"><a class="toclink" href="#bring-your-own-certificates">Bring Your Own Certificates</a></h2>
<p>You can also provide your own certificate files. Add these entries to your <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">./docker-data/dms/custom-certs/:/tmp/dms/custom-certs/:ro</span>
<span class="nt">environment</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">SSL_TYPE=manual</span>
<span class="c1"># Values should match the file paths inside the container:</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">SSL_CERT_PATH=/tmp/dms/custom-certs/public.crt</span>
<span class="p p-Indicator">-</span> <span class="l l-Scalar l-Scalar-Plain">SSL_KEY_PATH=/tmp/dms/custom-certs/private.key</span>
</code></pre></div>
<p>This will mount the path where your certificate files reside locally into the <em>read-only</em> container folder: <code>/tmp/dms/custom-certs</code>.</p>
<p>The local and internal paths may be whatever you prefer, so long as both <code>SSL_CERT_PATH</code> and <code>SSL_KEY_PATH</code> point to the correct internal file paths. The certificate files may also be named to your preference, but should be PEM encoded.</p>
<p><code>SSL_ALT_CERT_PATH</code> and <code>SSL_ALT_KEY_PATH</code> are additional ENV vars to support a 2nd certificate as a fallback. Commonly known as hybrid or dual certificate support. This is useful for using a modern ECDSA as your primary certificate, and RSA as your fallback for older connections. They work in the same manner as the non-<code>ALT</code> versions.</p>
<div class="admonition info">
<p class="admonition-title">Info</p>
<p>You may have to restart <code>docker-mailserver</code> once the certificates change.</p>
</div>
<h2 id="testing-a-certificate-is-valid"><a class="toclink" href="#testing-a-certificate-is-valid">Testing a Certificate is Valid</a></h2>
<ul>
<li>
<p>From your host:</p>
<div class="highlight"><pre><span></span><code>docker <span class="nb">exec</span> mailserver openssl s_client <span class="se">\</span>
-connect <span class="m">0</span>.0.0.0:25 <span class="se">\</span>
-starttls smtp <span class="se">\</span>
-CApath /etc/ssl/certs/
</code></pre></div>
</li>
<li>
<p>Or:</p>
<div class="highlight"><pre><span></span><code>docker <span class="nb">exec</span> mailserver openssl s_client <span class="se">\</span>
-connect <span class="m">0</span>.0.0.0:143 <span class="se">\</span>
-starttls imap <span class="se">\</span>
-CApath /etc/ssl/certs/
</code></pre></div>
</li>
</ul>
<p>And you should see the certificate chain, the server certificate and: <code>Verify return code: 0 (ok)</code></p>
<p>In addition, to verify certificate dates:</p>
<div class="highlight"><pre><span></span><code>docker <span class="nb">exec</span> mailserver openssl s_client <span class="se">\</span>
-connect <span class="m">0</span>.0.0.0:25 <span class="se">\</span>
-starttls smtp <span class="se">\</span>
-CApath /etc/ssl/certs/ <span class="se">\</span>
<span class="m">2</span>&gt;/dev/null <span class="p">|</span> openssl x509 -noout -dates
</code></pre></div>
<h2 id="plain-text-access"><a class="toclink" href="#plain-text-access">Plain-Text Access</a></h2>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>Not recommended for purposes other than testing.</p>
</div>
<p>Add this to <code>docker-data/dms/config/dovecot.cf</code>:</p>
<div class="highlight"><pre><span></span><code><span class="na">ssl</span> <span class="o">=</span> <span class="s">yes</span>
<span class="na">disable_plaintext_auth</span><span class="o">=</span><span class="s">no</span>
</code></pre></div>
<p>These options in conjunction mean:</p>
<ul>
<li>SSL/TLS is offered to the client, but the client isn't required to use it.</li>
<li>The client is allowed to login with plaintext authentication even when SSL/TLS isn't enabled on the connection.</li>
<li><strong>This is insecure</strong>, because the plaintext password is exposed to the internet.</li>
</ul>
<h2 id="importing-certificates-obtained-via-another-source"><a class="toclink" href="#importing-certificates-obtained-via-another-source">Importing Certificates Obtained via Another Source</a></h2>
<p>If you have another source for SSL/TLS certificates you can import them into the server via an external script. The external script can be found here: <a href="https://github.com/hanscees/dockerscripts/blob/master/scripts/tomav-renew-certs">external certificate import script</a>.</p>
<div class="admonition attention">
<p class="admonition-title">Only compatible with <code>docker-mailserver</code> releases &lt; <code>v10.2</code></p>
<p>The script expects <code>/etc/postfix/ssl/cert</code> and <code>/etc/postfix/ssl/key</code> files to be configured paths for both Postfix and Dovecot to use.</p>
<p>Since the <code>docker-mailserver</code> 10.2 release, certificate files have moved to <code>/etc/dms/tls/</code>, and the file name may differ depending on provisioning method.</p>
<p>This third-party script also has <code>fullchain.pem</code> and <code>privkey.pem</code> as hard-coded, thus is incompatible with other filenames.</p>
<p>Additionally it has never supported handling <code>ALT</code> fallback certificates (for supporting dual/hybrid, RSA + ECDSA).</p>
</div>
<p>The steps to follow are these:</p>
<ol>
<li>Transfer the new certificates to <code>./docker-data/dms/custom-certs/</code> (volume mounted to: <code>/tmp/ssl/</code>)</li>
<li>You should provide <code>fullchain.key</code> and <code>privkey.pem</code></li>
<li>Place the script in <code>./docker-data/dms/config/</code> (volume mounted to: <code>/tmp/docker-mailserver/</code>)</li>
<li>Make the script executable (<code>chmod +x tomav-renew-certs.sh</code>)</li>
<li>Run the script: <code>docker exec mailserver /tmp/docker-mailserver/tomav-renew-certs.sh</code></li>
</ol>
<p>If an error occurs the script will inform you. If not you will see both postfix and dovecot restart.</p>
<p>After the certificates have been loaded you can check the certificate:</p>
<div class="highlight"><pre><span></span><code>openssl s_client <span class="se">\</span>
-servername mail.example.com <span class="se">\</span>
-connect <span class="m">192</span>.168.0.72:465 <span class="se">\</span>
<span class="m">2</span>&gt;/dev/null <span class="p">|</span> openssl x509
<span class="c1"># or</span>
openssl s_client <span class="se">\</span>
-servername mail.example.com <span class="se">\</span>
-connect mail.example.com:465 <span class="se">\</span>
<span class="m">2</span>&gt;/dev/null <span class="p">|</span> openssl x509
</code></pre></div>
<p>Or you can check how long the new certificate is valid with commands like:</p>
<div class="highlight"><pre><span></span><code><span class="nb">export</span> <span class="nv">SITE_URL</span><span class="o">=</span><span class="s2">&quot;mail.example.com&quot;</span>
<span class="nb">export</span> <span class="nv">SITE_IP_URL</span><span class="o">=</span><span class="s2">&quot;192.168.0.72&quot;</span> <span class="c1"># can also use `mail.example.com`</span>
<span class="nb">export</span> <span class="nv">SITE_SSL_PORT</span><span class="o">=</span><span class="s2">&quot;993&quot;</span> <span class="c1"># imap port dovecot</span>
<span class="c1">##works: check if certificate will expire in two weeks </span>
<span class="c1">#2 weeks is 1209600 seconds</span>
<span class="c1">#3 weeks is 1814400</span>
<span class="c1">#12 weeks is 7257600</span>
<span class="c1">#15 weeks is 9072000</span>
<span class="nv">certcheck_2weeks</span><span class="o">=</span><span class="sb">`</span>openssl s_client -connect <span class="si">${</span><span class="nv">SITE_IP_URL</span><span class="si">}</span>:<span class="si">${</span><span class="nv">SITE_SSL_PORT</span><span class="si">}</span> <span class="se">\</span>
-servername <span class="si">${</span><span class="nv">SITE_URL</span><span class="si">}</span> <span class="m">2</span>&gt; /dev/null <span class="p">|</span> openssl x509 -noout -checkend <span class="m">1209600</span><span class="sb">`</span>
<span class="c1">####################################</span>
<span class="c1">#notes: output could be either:</span>
<span class="c1">#Certificate will not expire</span>
<span class="c1">#Certificate will expire</span>
<span class="c1">####################</span>
</code></pre></div>
<p>What does the script that imports the certificates do:</p>
<ol>
<li>Check if there are new certs in the internal container folder: <code>/tmp/ssl</code>.</li>
<li>Check with the ssl cert fingerprint if they differ from the current certificates.</li>
<li>If so it will copy the certs to the right places.</li>
<li>And restart postfix and dovecot.</li>
</ol>
<p>You can of course run the script by cron once a week or something. In that way you could automate cert renewal. If you do so it is probably wise to run an automated check on certificate expiry as well. Such a check could look something like this:</p>
<div class="highlight"><pre><span></span><code><span class="c1"># This script is run inside docker-mailserver via &#39;docker exec ...&#39;, using the &#39;mail&#39; command to send alerts.</span>
<span class="c1">## code below will alert if certificate expires in less than two weeks</span>
<span class="c1">## please adjust varables!</span>
<span class="c1">## make sure the &#39;mail -s&#39; command works! Test!</span>
<span class="nb">export</span> <span class="nv">SITE_URL</span><span class="o">=</span><span class="s2">&quot;mail.example.com&quot;</span>
<span class="nb">export</span> <span class="nv">SITE_IP_URL</span><span class="o">=</span><span class="s2">&quot;192.168.2.72&quot;</span> <span class="c1"># can also use `mail.example.com`</span>
<span class="nb">export</span> <span class="nv">SITE_SSL_PORT</span><span class="o">=</span><span class="s2">&quot;993&quot;</span> <span class="c1"># imap port dovecot</span>
<span class="c1"># Below can be from a different domain; like your personal email, not handled by this docker-mailserver:</span>
<span class="nb">export</span> <span class="nv">ALERT_EMAIL_ADDR</span><span class="o">=</span><span class="s2">&quot;external-account@gmail.com&quot;</span>
<span class="nv">certcheck_2weeks</span><span class="o">=</span><span class="sb">`</span>openssl s_client -connect <span class="si">${</span><span class="nv">SITE_IP_URL</span><span class="si">}</span>:<span class="si">${</span><span class="nv">SITE_SSL_PORT</span><span class="si">}</span> <span class="se">\</span>
-servername <span class="si">${</span><span class="nv">SITE_URL</span><span class="si">}</span> <span class="m">2</span>&gt; /dev/null <span class="p">|</span> openssl x509 -noout -checkend <span class="m">1209600</span><span class="sb">`</span>
<span class="c1">####################################</span>
<span class="c1">#notes: output can be</span>
<span class="c1">#Certificate will not expire</span>
<span class="c1">#Certificate will expire</span>
<span class="c1">####################</span>
<span class="c1">#echo &quot;certcheck 2 weeks gives $certcheck_2weeks&quot;</span>
<span class="c1">##automated check you might run by cron or something</span>
<span class="c1">## does the certificate expire within two weeks?</span>
<span class="k">if</span> <span class="o">[</span> <span class="s2">&quot;</span><span class="nv">$certcheck_2weeks</span><span class="s2">&quot;</span> <span class="o">=</span> <span class="s2">&quot;Certificate will not expire&quot;</span> <span class="o">]</span><span class="p">;</span> <span class="k">then</span>
<span class="nb">echo</span> <span class="s2">&quot;all is well, certwatch 2 weeks says </span><span class="nv">$certcheck_2weeks</span><span class="s2">&quot;</span>
<span class="k">else</span>
<span class="nb">echo</span> <span class="s2">&quot;Cert seems to be expiring pretty soon, within two weeks: </span><span class="nv">$certcheck_2weeks</span><span class="s2">&quot;</span>
<span class="nb">echo</span> <span class="s2">&quot;we will send an alert email and log as well&quot;</span>
logger Certwatch: cert <span class="nv">$SITE_URL</span> will expire <span class="k">in</span> two weeks
<span class="nb">echo</span> <span class="s2">&quot;Certwatch: cert </span><span class="nv">$SITE_URL</span><span class="s2"> will expire in two weeks&quot;</span> <span class="p">|</span> mail -s <span class="s2">&quot;cert </span><span class="nv">$SITE_URL</span><span class="s2"> expires in two weeks &quot;</span> <span class="nv">$ALERT_EMAIL_ADDR</span>
<span class="k">fi</span>
</code></pre></div>
<h2 id="custom-dh-parameters"><a class="toclink" href="#custom-dh-parameters">Custom DH Parameters</a></h2>
<p>By default <code>docker-mailserver</code> uses <a href="https://github.com/internetstandards/dhe_groups"><code>ffdhe4096</code></a> from <a href="https://datatracker.ietf.org/doc/html/rfc7919">IETF RFC 7919</a>. These are standardized pre-defined DH groups and the only available DH groups for TLS 1.3. It is <a href="https://crypto.stackexchange.com/questions/29926/what-diffie-hellman-parameters-should-i-use">discouraged to generate your own DH parameters</a> as it is often less secure.</p>
<p>Despite this, if you must use non-standard DH parameters or you would like to swap <code>ffdhe4096</code> for a different group (eg <code>ffdhe2048</code>); Add your own PEM encoded DH params file via a volume to <code>/tmp/docker-mailserver/dhparams.pem</code>. This will replace DH params for both Dovecot and Postfix services during container startup.</p>
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