OpenSMTPD is a free and open-source implementation of the Simple Mail Transfer Protocol (SMTP) that ships with some BSD operating systems, including OpenBSD. In this tutorial, you’ll learn how to install OpenSMTPD on Fedora CoreOS Latest, which is an operating system designed for running containerized applications.
Before you begin, make sure that you have the following:
The installation of OpenSMTPD is straightforward, and you can use the DNF package manager to install it. Connect to your Fedora CoreOS Latest instance and run the following command:
$ sudo dnf install opensmtpd
The command will install OpenSMTPD and all its dependencies.
After installing OpenSMTPD, you need to configure it to work with your environment. The configuration files are located in the /etc/opensmtpd/ directory. The main configuration file is smtpd.conf, which contains the configuration directives for the OpenSMTPD daemon.
Open the /etc/opensmtpd/smtpd.conf file with your favorite editor:
$ sudo nano /etc/opensmtpd/smtpd.conf
The first thing you need to do is to define the domains and IP addresses that OpenSMTPD will listen to for incoming connections. By default, OpenSMTPD listens on all network interfaces, but you can restrict it to specific interfaces.
In the smtpd.conf file, add the following directives to listen on all IP addresses and accept messages for the example.com domain:
listen on all port 25
accept from any for domain "example.com" alias "mail.example.com"
The default configuration of OpenSMTPD does not require authentication to send email. However, if you want to require authentication, you need to enable SMTP AUTH and configure the authentication mechanism.
To enable SMTP AUTH, add the following directive to the smtpd.conf file:
auth-optional
This directive will make authentication optional. If you want to require authentication, use the auth-required directive instead.
Next, you need to configure the authentication mechanism. OpenSMTPD supports various authentication mechanisms, such as PLAIN, LOGIN, and CRAM-MD5.
To configure the PLAIN authentication mechanism, add the following directives:
auth "auth_plain" {
passdb backend passwd
}
auth-plain "auth_plain"
These directives specify that the PLAIN authentication mechanism will use the passwd backend to store the passwords.
By default, OpenSMTPD is configured to deliver email locally. If you want to relay email to another SMTP server, you need to configure a relay.
To configure a relay, add the following directives to the smtpd.conf file:
table aliases file:/etc/aliases
action "relay" relay host smtp.gmail.com port 587 auth-optional tls auth-plain
match from any for domain <localhost> action "relay"
These directives specify that OpenSMTPD will use smtp.gmail.com as the relay host and the aliases file to alias local users. The relay will be secured with TLS and authentication using the LOGIN mechanism.
Note that these are just basic examples to get you started with OpenSMTPD. For a more comprehensive configuration, see the OpenSMTPD documentation.
Now that OpenSMTPD is installed and configured, you can start it by running the following command:
$ sudo systemctl enable --now opensmtpd
This command will start OpenSMTPD and enable it to start at boot.
In this tutorial, you learned how to install and configure OpenSMTPD on Fedora CoreOS Latest. With OpenSMTPD, you can set up your own SMTP server to send and receive email. Remember to keep your server secure and up to date with the latest patches and updates.
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