After the basic installation your server will reboot and allow you to login. You can either login at the console (if you have physical access to the system) or using SSH (secure shell).
Unless you just installed the server it is a good idea to install all missing updates first:
apt update apt upgrade
Let us install the necessary Debian packages to make it an actual mail server. You will install:
The MySQL server that will store information about your email accounts and domains. In previous versions this package was called “mysql-server”. MySQL was bought by SUN Microsystems which was later bought again by Oracle. Its original developer Monty was not happy with Oracle and thus maintained the software under the new name MariaDB. (Maria and My are the names of Monty’s children.) So basically MariaDB is a fork of MySQL. Both pieces of software started to evolve in slightly different directions. However Linux distributions decided to go with the most open-sourcy way thus choosing MariaDB. So basically MariaDB is what you knew as MySQL. The “other” MySQL is available directly from Oracle. I just wonder how much I trust a commercial database maker with sponsoring a competing open-source product.
The MTA (mail transport agent) that speaks SMTP and receives and sends emails.
An extension that allows Postfix to get its information from a MySQL database. (Yes, it’s compatible to MariaDB.)
The IMAP/POP3 mail server including an extension to query information from a MariaDB database.
An extension to Dovecot that allows users to fetch emails using the POP3 protocol. (This is optional. Only few users nowadays use POP3.)
An extension to Dovecot that allows users to access emails using the IMAP protocol.
Enables Dovecot to receive LMTP connections. We will need it later to make Postfix send emails to Dovecot for storage.
An extension to Dovecot that allows users to define filter rules that are automatically run on the server when a new email arrives.
- apache2 and php7.0
The web server that powers the webmail interface. PHP is the scripting language that the Roundcube webmail software is written in.
A web interface to manage your SQL database.
A third-party software that deals with spam and malware and handles automatic domain key signing.
A tool to create random passwords.
The SWiss Army Knife of Smtp. A utility to send emails through SMTP for testing purposes.
A console-based program that can speak IMAP and also read Maildirs directly. Very helpful for testing the functionality of your mail server.
A tool that talks to the LetsEncrypt certificate service to create and renew certificates.
A set of certificates from common certificate authorities on the internet. It is required for the proper function of wget for example.
A daemon that tracks log files to determine brute force attacks. It can block IP addresses of attackers. We will use it to defend against evil people trying to get into your mail server.
Let’s start with the pwgen utility. It helps you create secure passwords. Unless you already have a tool for that…
apt install pwgen
You will need a random passwords later to create a database user for the mail server. Just as an example: to create a secure password having a length of 20 characters you would run:
pwgen -s 20 1
That gets you a string like “W2EzNUFJzjEmA8tQT7A0”.
If you used MySQL before you may remember that you were forced to specify a password for the ‘root’ database user. That has changed with MariaDB in Debian – for the better. Now you can access the database server without any password if you are logged in as ‘root’ on the server. You might as well set a password but it is not necessary.
Go install the MariaDB server package:
apt install mariadb-server
If all went well you can now run “mysql” and get a connection to your MySQL database:
root@buster:~# mysql Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 30 Server version: 10.3.18-MariaDB-0+deb10u1 Debian 10 Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. MariaDB [(none)]>
Exit the SQL shell by typing “exit” or press CTRL-D.
Now on to the Postfix packages:
apt install postfix postfix-mysql
When you get asked for the mail server configuration type please choose “Internet site”. Enter your own mail server name (the fully qualified domain name) or just press enter. The host name and domain does not need to match any of your email domains.
Apache and PHP
To provide a webmail service you need the Apache web server software and the PHP scripting language support:
apt install apache2 php7.3
Just like in the Stretch guide we will deal with spam using rspamd. Since Debian Buster the software is included as a software package. So installing is as simple as:
apt install rspamd
A very useful tool to test email delivery later is SWAKS (the SWiss Army Knife for Smtp):
apt install swaks
This is a full-featured IMAP mail client. Think of it as a console-based Thunderbird. It cannot display HTML but it is very helpful to test IMAP mail servers. And some hardcore users still prefer it over any other mail client. Think of it as the vi of mail clients.
apt install mutt
You will want to use encrypted connections where possible. So you need a certificate for your services. The certbot software allows you to request and manage that certificate automatically.
apt install certbot
In addition to Postfix (that handles SMTP communication) you will need Dovecot to store received emails and provide IMAP (and optionally POP3) access for your users:
apt install dovecot-mysql dovecot-pop3d dovecot-imapd dovecot-managesieved dovecot-lmtpd
Adminer (replaces phpmyadmin)
SQL databases are called like that because SQL (structured query language) is the way you talk to it. But as we are just puny humans let’s have a more user-friendly interface to manage the database. Formerly I recommended phpmyadmin. But unfortunately it was excluded from the Debian Buster release.
So I looked around and found Adminer to be a lightweight, secure and featureful replacement.
apt install adminer
To avoid errors when downloading files using wget you should install the default set of certificates of common certificate authorities on the internet:
apt install ca-certificates