--- title: TLS certificate lastUpdated: 2025-11-01 slug: ispmail-trixie/tls-certificate sidebar: order: 158 --- import StepListReceive from "../../../components/StepListReceive.astro"; import { Aside } from "@astrojs/starlight/components"; Your mail server can't work properly without a valid TLS certificate. It will be used in three places: 1. the **webmail** interface (driven by the Apache web server) 2. **Postfix** (to encrypt SMTP communication with other mail servers on the internet where possible) 3. **Dovecot** (to encrypt IMAP/POP3 communication) Your mail server will be able to host email addresses for many domains. But a TLS certificate is usually issued for a single [FQDN](https://en.wikipedia.org/wiki/Fully_qualified_domain_name) like `mail.example.org`. That _common name_ is an important part of the certificate. It must match the name your users use to talk to the server. **Correct**: Your mail server is addressed as `mail.example.org`. The TLS certificate was also issued to `mail.example.org`. **Wrong**: Your mail server is addressed as `smtp01.example.com`. But the TLS certificate was issued to `mail.example.org`. So choose an FQDN for your mail server. For example I use `webmail.workaround.org` for my personal server. ## Certbot You already have the `certbot` software and the `apache2` web server installed. Requesting a certificate from Let's Encrypt is as simple as running the next command. ```sh title="Run this on your server" certbot --apache --register-unsafely-without-email --agree-tos -d mail.example.org ```
Click here to learn what the options mean… - **--apache**: Use the [HTTP challenge](https://letsencrypt.org/docs/challenge-types/) to verify that you are actually in control of the FQDN. The certbot plugin will add some configuration to intercept HTTP requests to `/.well-known/acme-challenge/…` on your web server. This is a fully automatic process that does not even have to stop your web server. - **--register-unsafely-without-email**: Do not ask for an email address to send to Let's Encrypt. Before June 2025 Let's Encrypt used that address to inform you if your certificate is about to expire and the automatic renewal failed. Nowadays they do not need an email any more. But for historical reasons they still ask for it by default. - **--agree-tos**: Confirm that you have read Let's Encrypt's terms and conditions. Let's be honest – nobody reads that. - **-d**: The domain that the certificate will be issued to. This has to be the exact FQDN of your server.
The output should look like: ``` Saving debug log to /var/log/letsencrypt/letsencrypt.log Requesting a certificate for mail.example.org Successfully received certificate. Certificate is saved at: /etc/letsencrypt/live/mail.example.org/fullchain.pem Key is saved at: /etc/letsencrypt/live/mail.example.org/privkey.pem This certificate expires on 2025-11-22. These files will be updated when the certificate renews. Certbot has set up a scheduled task to automatically renew this certificate in the background. Deploying certificate Successfully deployed certificate for mail.example.org to /etc/apache2/sites-available/000-default-le-ssl.conf Congratulations! You have successfully enabled HTTPS on https://mail.example.org - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - If you like Certbot, please consider supporting our work by: * Donating to ISRG / Let's Encrypt: https://letsencrypt.org/donate * Donating to EFF: https://eff.org/donate-le - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ```
Click here to learn which files have been created… In /etc/letsencrypt/live/**mail.example.org** you will find a couple of files now: - **cert.pem**: the certificate file - **chain.pem**: the _chaining_ or _intermediate_ certificate. This certificate provides information how the LetsEncrypt certificates are linked to other known certificate authorities. It is generally a good idea to always send this certificate along with your own for clients who may not know LetsEncrypt properly yet. - **fullchain.pem**: this file contains a concatenation of the _cert.pem_ and the _chain.pem_. This is the preferred file to use when a piece of software asks where to find the _certificate_. - **privkey.pem**: the private key file. Keep it secret. Well, actually those are not files but _symbolic links_ pointing to the "archive" directory. But don't worry about that.
## Renewal Your new certificate is only valid for 3 months. Fortunately the renewal is happening automatically. A _systemd timer_ checks your certificate frequently and triggers a renewal one month before it expires. It is important that services that use the certificate load the new certificate after an automatic renewal. This shell command will create a file `/etc/letsencrypt/cli.ini` that handles it: ```sh title="Run this on your server" echo > /etc/letsencrypt/cli.ini "post-hook = systemctl reload postfix dovecot apache2" ``` Perfect. You won't have to worry about the certificate again.
Click here to learn how the renewal works… These commands will show you the definition and status of the timer and the renewal service: ```sh title="Run this on your server" systemctl status certbot.timer systemctl cat certbot.timer systemctl status certbot.service systemctl cat certbot.service ``` _Systemd timers_ are similar to cron jobs. They require more work to set up but have some nice features and make you look cooler.