How to Add Mail User Accounts Using Virtual Users on AlmaLinux

Managing mail servers efficiently is a critical task for server administrators. In many cases, using virtual users to handle email accounts is preferred over creating system users. Virtual users allow you to separate mail accounts from system accounts, providing flexibility, enhanced security, and streamlined management.

In this guide, we’ll walk you through how to set up and manage mail user accounts using virtual users on AlmaLinux, a popular enterprise Linux distribution. By the end, you’ll be able to create, configure, and manage virtual mail users effectively.

What Are Virtual Mail Users?

Virtual mail users are email accounts that exist solely for mail purposes and are not tied to system users. They are managed independently of the operating system’s user database, providing benefits such as:

• Enhanced security (no direct shell access for mail users).
• Easier account management for mail-only users.
• Greater scalability for hosting multiple domains or users.

Prerequisites

Before starting, ensure you have the following in place:

1. A server running AlmaLinux.
2. Postfix and Dovecot installed and configured as your Mail Transfer Agent (MTA) and Mail Delivery Agent (MDA), respectively.
3. Root or sudo access to the server.

Step 1: Install Required Packages

Begin by ensuring your AlmaLinux system is updated and the necessary mail server components are installed:

Update System Packages

sudo dnf update -y

Install Postfix and Dovecot

sudo dnf install postfix dovecot -y

Install Additional Tools

For virtual user management, you’ll need tools like mariadb-server or sqlite to store user data, and other dependencies:

sudo dnf install mariadb-server mariadb postfix-mysql -y

Start and enable MariaDB:

sudo systemctl start mariadb
sudo systemctl enable mariadb

Step 2: Configure the Database for Virtual Users

Virtual users and domains are typically stored in a database. You can use MariaDB to manage this.

Step 2.1: Secure MariaDB Installation

Run the secure installation script:

sudo mysql_secure_installation

Follow the prompts to set a root password and secure your database server.

Step 2.2: Create a Database and Tables

Log in to MariaDB:

sudo mysql -u root -p

Create a database for mail users:

CREATE DATABASE mailserver;

Switch to the database:

USE mailserver;

Create tables for virtual domains, users, and aliases:

CREATE TABLE virtual_domains (
    id INT NOT NULL AUTO_INCREMENT,
    name VARCHAR(50) NOT NULL,
    PRIMARY KEY (id)
);

CREATE TABLE virtual_users (
    id INT NOT NULL AUTO_INCREMENT,
    domain_id INT NOT NULL,
    password VARCHAR(255) NOT NULL,
    email VARCHAR(100) NOT NULL,
    PRIMARY KEY (id),
    UNIQUE KEY email (email),
    FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE
);

CREATE TABLE virtual_aliases (
    id INT NOT NULL AUTO_INCREMENT,
    domain_id INT NOT NULL,
    source VARCHAR(100) NOT NULL,
    destination VARCHAR(100) NOT NULL,
    PRIMARY KEY (id),
    FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE
);

Step 2.3: Add Sample Data

Insert a virtual domain and user for testing:

INSERT INTO virtual_domains (name) VALUES ('example.com');

INSERT INTO virtual_users (domain_id, password, email)
VALUES (1, ENCRYPT('password'), 'user@example.com');

Exit the database:

EXIT;

Step 3: Configure Postfix for Virtual Users

Postfix needs to be configured to fetch virtual user information from the database.

Step 3.1: Install and Configure Postfix

Edit the Postfix configuration file:

sudo nano /etc/postfix/main.cf

Add the following lines for virtual domains and users:

virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf

Step 3.2: Create Postfix MySQL Configuration Files

Create configuration files for each mapping.

/etc/postfix/mysql-virtual-mailbox-domains.cf:

user = mailuser
password = mailpassword
hosts = 127.0.0.1
dbname = mailserver
query = SELECT name FROM virtual_domains WHERE name='%s'

/etc/postfix/mysql-virtual-mailbox-maps.cf:

user = mailuser
password = mailpassword
hosts = 127.0.0.1
dbname = mailserver
query = SELECT email FROM virtual_users WHERE email='%s'

/etc/postfix/mysql-virtual-alias-maps.cf:

user = mailuser
password = mailpassword
hosts = 127.0.0.1
dbname = mailserver
query = SELECT destination FROM virtual_aliases WHERE source='%s'

Replace mailuser and mailpassword with the credentials you created for your database.

Set proper permissions:

sudo chmod 640 /etc/postfix/mysql-virtual-*.cf
sudo chown postfix:postfix /etc/postfix/mysql-virtual-*.cf

Reload Postfix:

sudo systemctl restart postfix

Step 4: Configure Dovecot for Virtual Users

Dovecot handles mail retrieval for virtual users.

Step 4.1: Edit Dovecot Configuration

Open the main Dovecot configuration file:

sudo nano /etc/dovecot/dovecot.conf

Enable mail delivery for virtual users by adding:

mail_location = maildir:/var/mail/vhosts/%d/%n
namespace inbox {
    inbox = yes
}

Step 4.2: Set up Authentication

Edit the authentication configuration:

sudo nano /etc/dovecot/conf.d/auth-sql.conf.ext

Add the following:

passdb {
    driver = sql
    args = /etc/dovecot/dovecot-sql.conf.ext
}

userdb {
    driver = static
    args = uid=vmail gid=vmail home=/var/mail/vhosts/%d/%n
}

Create /etc/dovecot/dovecot-sql.conf.ext:

driver = mysql
connect = host=127.0.0.1 dbname=mailserver user=mailuser password=mailpassword
default_pass_scheme = MD5-CRYPT
password_query = SELECT email as user, password FROM virtual_users WHERE email='%u';

Set permissions:

sudo chmod 600 /etc/dovecot/dovecot-sql.conf.ext
sudo chown dovecot:dovecot /etc/dovecot/dovecot-sql.conf.ext

Reload Dovecot:

sudo systemctl restart dovecot

Step 5: Add New Virtual Users

You can add new users directly to the database:

USE mailserver;

INSERT INTO virtual_users (domain_id, password, email)
VALUES (1, ENCRYPT('newpassword'), 'newuser@example.com');

Ensure the user directory exists:

sudo mkdir -p /var/mail/vhosts/example.com/newuser
sudo chown -R vmail:vmail /var/mail/vhosts

Step 6: Testing the Configuration

Test email delivery using tools like telnet or mail clients:

telnet localhost 25

Ensure that emails can be sent and retrieved.

Conclusion

Setting up virtual mail users on AlmaLinux offers flexibility, scalability, and security for managing mail services. By following this guide, you can configure a database-driven mail system using Postfix and Dovecot, allowing you to efficiently manage email accounts for multiple domains.

With this setup, your server is equipped to handle email hosting for various scenarios, from personal projects to business-critical systems.