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-title: Dovecot SSL Certificate Renewal
-date: May 12, 2021 11:06
----
-<p>
-Just a quick technical note.
-</p>
-
-<p>
-As mentioned before, I
-<a href='<%= path_to "blog_hosting-on-vultr-vps" %>'>
-  started self hosting email
-</a> a while ago. Exactly three months ago, in fact, and I know this because
-that's how long Let's Encrypt SSL certificates are valid
-for. Yesterday, my email clients started complaining about an invalid
-certificate coming from my mail server.
-</p>
-
-<p>
-After a few minutes of worrying if I'm being man-in-the-middled, I ssh'd into my
-VPS to debug.
-</p>
-
-<h3>TL;DR: Root cause and solution</h3>
-<p>
-Turns out when configuring Dovecot (the IMAP server I use), the SSL certificate
-you set is just a static string, not a filename pointing to a file that Dovecot
-will read every time it needs to serve it. As such, even after Certbot correctly
-got a new certificate, Dovecot was still using the old one.
-</p>
-
-<p>
-This can be fixed by restarting Dovecot, allowing it to read the new
-certificate, assuming its available at the same path.
-</p>
-
-<h4>Long term solution</h4>
-<p>
-I already have a cronjob that runs <code>certbot renew</code> once a month to
-renew any SSL certificates going stale. I'm going to change it to instead point
-to a script that does
-
-<pre>
-certbot renew
-systemctl restart dovecot
-</pre>
-
-to automate reloading the certificate.
-</p>
-
-<h3>Learnings</h3>
-<p>
-A few things I learned while debugging this issue:
-</p>
-
-<h4>Viewing certificate info on the command line</h4>
-<p>
-My first step was to check the certificate I thought should have been served by
-Dovecot. In particular, I wanted to see its expiry date as well as compare its
-fingerprint to that reported by my mail client.
-</p>
-
-<p>
-Certificates are stored in ASCII armor format, which is not human readable.
-Turns out you can get a human readable interpretation of your certificate with
-the <code>openssl</code> CLI tool:
-
-<pre>
-openssl x509 -text -noout -in &lt;certificate file&gt;
-</pre>
-
-will get you a detailed, human readable output. For example, you can find a
-"Validity" section, specifying the time period during which the certificate is
-valid.
-</p>
-
-<p>
-Adding the <code>-fingerprint</code> flag will also output the fingerprint hash.
-The <code>-noout</code> flag is just there to suppress the output of the
-non-readable ASCII armor text.
-</p>
-
-<h4>Let's Encrypt certificate locations</h4>
-<p>
-Currently valid certificates from Let's Encrypt are stored under
-<code>/etc/letsencrypt/live/&lt;domain name&gt;/</code>. This is where my
-Dovecot server was configured to get its certificate from, so before I realized
-that the certificate is only read once, I was surprised that the fingerprint of
-the certificate stored here did not match the one my mail client was receiving.
-</p>
-
-<p>
-Turns out Let's Encrypt also stores historic certificates under
-<code>/etc/letsencrypt/archive/</code>. Here I was able to find the certificate
-with a matching fingerprint to the faulty one received by my client, and confirm
-that it did indeed expire yesterday. Finding this is what led me to realizing
-how Dovecot handles its certificate configuration.
-</p>