Part 3: PostfixAdmin – Create Virtual Mailboxes on Ubuntu 20.04 Mail Server

In previous articles, we discussed how to set up your own mail server on Ubuntu from scratch. In part 1 and part 2 of this tutorial series, we learned how to set up Postfix SMTP server and Dovecot IMAP server, but so far we can only have email addresses for users with local Unix accounts. This tutorial is going to show you how to create virtual mailboxes on Ubuntu 20.04 mail server with PostfixAdmin, which is an open-source web-based interface to configure and manage a Postfix based email server for many domains and users.

With virtual mailboxes, we don’t need to create a local Unix account for each email address. If you are going to set up a mail server for a company or organization, it’s always better to have an easy way to create virtual mailboxes in a web-based interface, which also allows users to change their passwords. That’s where PostfixAdmin comes in.

PostfixAdmin Features

• manage mailboxes, virtual domains and aliases
• vacation/out-of-office messages
• alias domains (forwarding one domain to another with recipient validation)
• users can manage their own mailbox (change alias, password and vacation message)
• quota support for single mailboxes and total quota of a domain
• display used quota
• fetchmail integration: You can fetch emails from your original email address to your new email address.
• command line client postfixadmin-cli for those who don’t want to click around in a web interface 😉

Note: Once you finish part 3, you can no longer use local Unix accounts as email addresses. You must create email addresses from the PostfixAdmin web interface.

Prerequisites

It’s required that you have followed part 1 and part 2 of this tutorial series before continuing reading this article. If you followed mail server tutorials on other websites, I recommend purging your configurations and start over with my tutorial series, so you are not going to be confused by different setup processes.

PostfixAdmin is written in PHP and requires a database (MySQL/MariaDB, PostgreSQL or SQLite). This article will use MariaDB database. You also need to run Apache or Nginx web server. So basically we are going to need a LAMP or LEMP stack.

If you prefer to use Apache web server, then set up a LAMP stack.

• How to set up LAMP stack on Ubuntu 20.04

If you prefer to use Nginx web server, then set up a LEMP stack.

• How to set up LEMP stack on Ubuntu 20.04

Once the above requirements are met, let’s install and configure PostfixAdmin.

Step 1: Install PostfixAdmin on Ubuntu 20.04 Server

Log into your mail server. Because some readers use MariaDB server, while others use MySQL, which makes things complicated, so before installing PostfixAdmin, we install the dbconfig-no-thanks package to prevent the postfixadmin package from launching the database configure wizard.

sudo apt install dbconfig-no-thanks

Then install PostfixAdmin from the default Ubuntu software repository.

sudo apt install postfixadmin

Note: If you have previously installed mysql-server on Ubuntu, the installation of PostfixAdmin will probably remove the mysql-server package from your system. You can re-install it by running the following command.

sudo apt install mysql-server

Now we need to remove the dbconfig-no-thanks package.

sudo apt remove dbconfig-no-thanks

Then launch the database configure wizard for PostfixAdmin.

sudo dpkg-reconfigure postfixadmin

During the installation, you will be asked if you want to reinstall database for PostfixAdmin. Press the Tab key to choose Yes.

Then select the default database type: mysql, if you use MySQL or MariaDB.

Next, choose the default connection method: Unix socket.

Then choose the default authentication plugin for MySQL/MariaDB.

Press Enter to choose the default database name for PostfixAdmin.

Press Enter to choose the default database username for PostfixAdmin.

After that, you need to set a password for this user. Note that the password should not contain the # character, or you might not be able to log in later.

Finally, choose the default database administrative user.

After PostfixAdmin is installed, you can log in to MySQL/MariaDB console with the following command. You will need to enter the password for the postfixadmin user.

mysql -u postfixadmin -p

And you can check what databases the user has permissions to access with the following command.

SHOW DATABASES;

Output:

+--------------------+
| Database           |
+--------------------+
| information_schema |
| postfixadmin       |
+--------------------+
2 rows in set (0.002 sec)

By default, the postfixadmin database contains no tables. You can log out of the MySQL/MariaDB console with the following command.

EXIT;

The installation will also create two configuration files: /etc/dbconfig-common/postfixadmin.conf and /etc/postfixadmin/dbconfig.inc.php, both of which contain the database access settings, including the database username and password. We need to change the database type from mysql to mysqli in both of the two files.

sudo nano /etc/dbconfig-common/postfixadmin.conf

Change

dbc_dbtype='mysql'

to

dbc_dbtype='mysqli'

Then edit the second file.

sudo nano /etc/postfixadmin/dbconfig.inc.php

Change

$dbtype='mysql';

to

$dbtype='mysqli';

The web files are installed under /usr/share/postfixadmin/ directory, which is owned by root. PostfixAdmin requires a templates_c directory, so create it.

sudo mkdir /usr/share/postfixadmin/templates_c

We need to give www-data user read, write and execute permissions on this directory with the following command.

sudo setfacl -R -m u:www-data:rwx /usr/share/postfixadmin/templates_c/

If your system can’t find the setfacl command, you need to install the acl package.

sudo apt install acl

Step 2: Create Apache Virtual Host or Nginx Config File for PostfixAdmin

Apache

If you use Apache web server, create a virtual host for PostfixAdmin.

sudo nano /etc/apache2/sites-available/postfixadmin.conf

Put the following text into the file. Replace postfixadmin.example.com with your real domain name and don’t forget to set DNS A record for it.

<VirtualHost *:80>
  ServerName postfixadmin.example.com
  DocumentRoot /usr/share/postfixadmin/public

  ErrorLog ${APACHE_LOG_DIR}/postfixadmin_error.log
  CustomLog ${APACHE_LOG_DIR}/postfixadmin_access.log combined

  <Directory />
    Options FollowSymLinks
    AllowOverride All
  </Directory>

  <Directory /usr/share/postfixadmin/>
    Options FollowSymLinks MultiViews
    AllowOverride All
    Order allow,deny
    allow from all
  </Directory>

</VirtualHost>

Save and close the file. Then enable this virtual host with:

sudo a2ensite postfixadmin.conf

Reload Apache for the changes to take effect.

sudo systemctl reload apache2

Now you should be able to see the PostfixAdmin web-based install wizard at http://postfixadmin.example.com/setup.php.

Nginx

If you use Nginx web server, create a virtual host for PostfixAdmin.

sudo nano /etc/nginx/conf.d/postfixadmin.conf

Put the following text into the file. Replace postfixadmin.example.com with your real domain name and don’t forget to set DNS A record for it.

server {
   listen 80;
   listen [::]:80;
   server_name postfixadmin.example.com;

   root /usr/share/postfixadmin/public/;
   index index.php index.html;

   access_log /var/log/nginx/postfixadmin_access.log;
   error_log /var/log/nginx/postfixadmin_error.log;

   location / {
       try_files $uri $uri/ /index.php;
   }

   location ~ ^/(.+\.php)$ {
        try_files $uri =404;
        fastcgi_pass unix:/run/php/php7.4-fpm.sock;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        include /etc/nginx/fastcgi_params;
   }
}

Save and close the file. Then test Nginx configuration.

sudo nginx -t

If the test is successful, reload Nginx for the changes to take effect.

sudo systemctl reload nginx

Now you should be able to see the PostfixAdmin web-based install wizard at http://postfixadmin.example.com/setup.php.

Step 3: Install Required and Recommended PHP Modules

Run the following command to install PHP modules required or recommended by PostfixAdmin.

sudo apt install php7.4-fpm php7.4-imap php7.4-mbstring php7.4-mysql php7.4-json php7.4-curl php7.4-zip php7.4-xml php7.4-bz2 php7.4-intl php7.4-gmp

Then restart Apache. (If you use Nginx, you don’t need to restart Nginx.)

sudo systemctl restart apache2

Step 4: Enabling HTTPS

To encrypt the HTTP traffic, we can enable HTTPS by installing a free TLS certificate issued from Let’s Encrypt. Run the following command to install Let’s Encrypt client (certbot) on Ubuntu 20.04 server.

sudo apt install certbot

If you use Apache, install the Certbot Apache plugin.

sudo apt install python3-certbot-apache

And run this command to obtain and install TLS certificate.

sudo certbot --apache --agree-tos --redirect --hsts --staple-ocsp --email [email protected] -d postfixadmin.example.com

If you use Nginx, then you also need to install the Certbot Nginx plugin.

sudo apt install python3-certbot-nginx

Next, run the following command to obtain and install TLS certificate.

sudo certbot --nginx --agree-tos --redirect --hsts --staple-ocsp --email [email protected] -d postfixadmin.example.com

Where

• --nginx: Use the nginx plugin.
• --apache: Use the Apache plugin.
• --agree-tos: Agree to terms of service.
• --redirect: Force HTTPS by 301 redirect.
• --hsts: Add the Strict-Transport-Security header to every HTTP response. Forcing browser to always use TLS for the domain. Defends against SSL/TLS Stripping.
• --staple-ocsp: Enables OCSP Stapling. A valid OCSP response is stapled to the certificate that the server offers during TLS.

The certificate should now be obtained and automatically installed, which is indicated by the message below.

Step 5: Use Strong Password Scheme in PostfixAdmin and Dovecot

By default, PostfixAdmin and Dovecot use MD5-CRYPT, which is a weak password scheme. You can list available password schemes in Dovecot with the following command.

sudo doveadm pw -l

Sample output:

SHA1 SSHA512 BLF-CRYPT PLAIN HMAC-MD5 OTP SHA512 SHA RPA DES-CRYPT CRYPT SSHA MD5-CRYPT SKEY PLAIN-MD4 PLAIN-MD5 SCRAM-SHA-1 LANMAN SHA512-CRYPT CLEAR CLEARTEXT ARGON2I ARGON2ID SSHA256 NTLM MD5 PBKDF2 SHA256 CRAM-MD5 PLAIN-TRUNC SHA256-CRYPT SMD5 DIGEST-MD5 LDAP-MD5

Argon2 is a fairly strong password scheme. To use it, we need to edit the PostfixAdmin configuration file, which by default is /usr/share/postfixadmin/config.inc.php, but we can create a separate file (config.local.php) to store our modifications, so they won’t be overriden when a new version of PostfixAdmin is installed in the future.

sudo nano /usr/share/postfixadmin/config.local.php

Add the following lines in the file to use Argon2 password scheme.

<?php
$CONF['encrypt'] = 'dovecot:ARGON2I';

$CONF['dovecotpw'] = "/usr/bin/doveadm pw -r 5";
if(@file_exists('/usr/bin/doveadm')) { // @ to silence openbase_dir stuff; see https://github.com/postfixadmin/postfixadmin/issues/171
    $CONF['dovecotpw'] = "/usr/bin/doveadm pw -r 5"; # debian
}

Save and close the file. We can also create a symlink in the /etc/postfixadmin/ directory, just in case PostfixAdmin can’t find the file.

sudo ln -s /usr/share/postfixadmin/config.local.php /etc/postfixadmin/config.local.php

We will configure password scheme for Dovecot in step 9.

Step 6: Finish the Installation in Web Browser

Go to postfixadmin.example.com/setup.php to run the web-based setup wizard. First, it will check if all dependencies are installed.

If you see the following error,

Invalid query: Specified key was too long; max key length is 1000 bytes

Then you need to log in to MySQL/MariaDB database server as root from command line,

sudo mysql -u root

and change the default collation from utf8mb4_general_ci to utf8_general_ci.

MariaDB [(none)]> alter database postfixadmin collate ='utf8_general_ci';

Exit MySQL/MariaDB console and reload the setup.php page. Once all requirements are satisfied, you can create a setup password for PostfixAdmin.

After creating the password hash, you need to open the /usr/share/postfixadmin/config.local.php file and add the setup password hash at the end of the file like below.

$CONF['setup_password'] = 'c8b5ddasdfawere1cb15:2a055d9ceed4657faghh3f4349597jmuk67cfafa';

Next, create the admin account.

After that, you can log into PostfixAdmin at postfixadmin.example.com/login.php.

Step 7: Checking Tables in the Database

The PostfixAdmin setup process populates the postfixadmin database with some default tables. It’s helpful for us to know the names and structure of the tables. Log in to MySQL/MariaDB console.

sudo mysql -u root

Select the postfixadmin database.

USE postfixadmin;

List all tables in this database.

SHOW TABLES;

Output:

+------------------------+
| Tables_in_postfixadmin |
+------------------------+
| admin                  |
| alias                  |
| alias_domain           |
| config                 |
| domain                 |
| domain_admins          |
| fetchmail              |
| log                    |
| mailbox                |
| quota                  |
| quota2                 |
| vacation               |
| vacation_notification  |
+------------------------+
13 rows in set (0.001 sec)

The 3 most important tables are:

• domain: contains information on the domains that are using your mail server to send and receive email.
• mailbox: contains information on every email address, including hashed password and the location of mail files.
• alias: contains the alias of each email address.

If you are interested, you can check what columns each table contains. For example, the following command will show us the columns in the domain table.

DESCRIBE domain;

Output:

+-------------+--------------+------+-----+---------------------+-------+
| Field       | Type         | Null | Key | Default             | Extra |
+-------------+--------------+------+-----+---------------------+-------+
| domain      | varchar(255) | NO   | PRI | NULL                |       |
| description | varchar(255) | NO   |     | NULL                |       |
| aliases     | int(10)      | NO   |     | 0                   |       |
| mailboxes   | int(10)      | NO   |     | 0                   |       |
| maxquota    | bigint(20)   | NO   |     | 0                   |       |
| quota       | bigint(20)   | NO   |     | 0                   |       |
| transport   | varchar(255) | NO   |     | NULL                |       |
| backupmx    | tinyint(1)   | NO   |     | 0                   |       |
| created     | datetime     | NO   |     | 2000-01-01 00:00:00 |       |
| modified    | datetime     | NO   |     | 2000-01-01 00:00:00 |       |
| active      | tinyint(1)   | NO   |     | 1                   |       |
+-------------+--------------+------+-----+---------------------+-------+

Log out of MySQL/MariaDB console.

EXIT;

Step 8: Configure Postfix to Use MySQL/MariaDB Database

By default, Postfix delivers emails only to users with a local Unix account. To make it deliver emails to virtual users whose information is stored in the database, we need to configure Postfix to use virtual mailbox domains.

First, we need to add MySQL map support for Postfix by installing the postfix-mysql package.

sudo apt install postfix-mysql

Then edit the Postfix main configuration file.

sudo nano /etc/postfix/main.cf

Add the following lines at the end of this file.

virtual_mailbox_domains = proxy:mysql:/etc/postfix/sql/mysql_virtual_domains_maps.cf
virtual_mailbox_maps =
   proxy:mysql:/etc/postfix/sql/mysql_virtual_mailbox_maps.cf,
   proxy:mysql:/etc/postfix/sql/mysql_virtual_alias_domain_mailbox_maps.cf
virtual_alias_maps =
   proxy:mysql:/etc/postfix/sql/mysql_virtual_alias_maps.cf,
   proxy:mysql:/etc/postfix/sql/mysql_virtual_alias_domain_maps.cf,
   proxy:mysql:/etc/postfix/sql/mysql_virtual_alias_domain_catchall_maps.cf

Where:

• virtual_mailbox_domains points to a file that will tell Postfix how to look up domain information from the database.
• virtual_mailbox_maps points to files that will tell Postfix how to look up email addresses from the database.
• virtual_alias_maps points to files that will tell Postfix how to look up aliases from the database.

We want to use dovecot to deliver incoming emails to the virtual users’ message store, so add the following line.

virtual_transport = lmtp:unix:private/dovecot-lmtp

Save and close the file. Next, we need to create the .cf files one by one. Create the sql directory.

sudo mkdir /etc/postfix/sql/

Create the mysql_virtual_domains_maps.cf file.

sudo nano /etc/postfix/sql/mysql_virtual_domains_maps.cf

Add the following content. Replace password with the postfixadmin password you set in Step 1.

user = postfixadmin
password = password
hosts = localhost
dbname = postfixadmin
query = SELECT domain FROM domain WHERE domain='%s' AND active = '1'
#query = SELECT domain FROM domain WHERE domain='%s'
#optional query to use when relaying for backup MX
#query = SELECT domain FROM domain WHERE domain='%s' AND backupmx = '0' AND active = '1'
#expansion_limit = 100

Create the mysql_virtual_mailbox_maps.cf file.

sudo nano /etc/postfix/sql/mysql_virtual_mailbox_maps.cf

Add the following content.

user = postfixadmin
password = password
hosts = localhost
dbname = postfixadmin
query = SELECT maildir FROM mailbox WHERE username='%s' AND active = '1'
#expansion_limit = 100

Create the mysql_virtual_alias_domain_mailbox_maps.cf file.

sudo nano /etc/postfix/sql/mysql_virtual_alias_domain_mailbox_maps.cf

Add the following content.

user = postfixadmin
password = password
hosts = localhost
dbname = postfixadmin
query = SELECT maildir FROM mailbox,alias_domain WHERE alias_domain.alias_domain = '%d' and mailbox.username = CONCAT('%u', '@', alias_domain.target_domain) AND mailbox.active = 1 AND alias_domain.active='1'

Create the mysql_virtual_alias_maps.cf file.

sudo nano /etc/postfix/sql/mysql_virtual_alias_maps.cf

Add the following content.

user = postfixadmin
password = password
hosts = localhost
dbname = postfixadmin
query = SELECT goto FROM alias WHERE address='%s' AND active = '1'
#expansion_limit = 100

Create the mysql_virtual_alias_domain_maps.cf file.

sudo nano /etc/postfix/sql/mysql_virtual_alias_domain_maps.cf

Add the following content.

user = postfixadmin
password = password
hosts = localhost
dbname = postfixadmin
query = SELECT goto FROM alias,alias_domain WHERE alias_domain.alias_domain = '%d' and alias.address = CONCAT('%u', '@', alias_domain.target_domain) AND alias.active = 1 AND alias_domain.active='1'

Create the mysql_virtual_alias_domain_catchall_maps file.

sudo nano /etc/postfix/sql/mysql_virtual_alias_domain_catchall_maps.cf

Add the following content.

# handles catch-all settings of target-domain
user = postfixadmin
password = password
hosts = localhost
dbname = postfixadmin
query = SELECT goto FROM alias,alias_domain WHERE alias_domain.alias_domain = '%d' and alias.address = CONCAT('@', alias_domain.target_domain) AND alias.active = 1 AND alias_domain.active='1'

Since the database passwords are stored in plain text so they should be readable only by user postfix and root, which is done by executing the following two commands.

sudo chmod 0640 /etc/postfix/sql/*
sudo setfacl -R -m u:postfix:rx /etc/postfix/sql/

Now let’s open the Postfix main configuration file again.

sudo nano /etc/postfix/main.cf

Find the mydestination parameter, which contains a list of domain names that will receive emails delivered to local Unix accounts. Since we are going to use virtual mailbox, so we need to remove the apex domain name from the list. My apex domain name is linuxbabe.com, so I removed it from the mydestination parameter.

mydestination = $myhostname, mail.linuxbabe.com, localhost.linuxbabe.com, localhost

Then add the following lines at the end of this file.

virtual_mailbox_base = /var/vmail
virtual_minimum_uid = 2000
virtual_uid_maps = static:2000
virtual_gid_maps = static:2000

The first line defines the base location of mail files. The remaining 3 lines define which user ID and group ID Postfix will use when delivering incoming emails to the mailbox. We use the user ID 2000 and group ID 2000.

Save and close the file. Restart Postfix for the changes to take effect.

sudo systemctl restart postfix

Next, we need to create a user named vmail with ID 2000 and a group with ID 2000.

sudo adduser vmail --uid 2000 --disabled-login --disabled-password

Create the mail base location.

sudo mkdir /var/vmail/

Make vmail as the owner.

sudo chown vmail:vmail /var/vmail/ -R

Step 9: Configure Dovecot to Use MySQL/MariaDB Database

We also need to configure the Dovecot IMAP server to query user information from the database. First, run the following command to add MySQL support for Dovecot.

sudo apt install dovecot-mysql

Then edit the 10-mail.conf file.

sudo nano /etc/dovecot/conf.d/10-mail.conf

In part 2, we used the default mail_location.

mail_location = mbox:~/mail:INBOX=/var/mail/%u

Since we are using virtual mailbox domain now, we need to change the mail_location to:

mail_location = maildir:/var/vmail/%d/%n

It’s recommended to enable mail_home for the virtual users by adding the following line in the file, because virtual users don’t have home directories by default.

mail_home = /var/vmail/%d/%n

Save and close the file. Then edit the 10-auth.conf file.

sudo nano /etc/dovecot/conf.d/10-auth.conf

In part 2, we used the following value for auth_username_format.

auth_username_format = %n

The %n would drop away the domain if it was given. Because in part 2 we were using local Unix account for the username of every email address, we must use %n to drop away the domain, so users were able to login with the full email address.

Now we are using virtual mailbox domains, which means the username of every email address includes the domain part, so we need to change the auth_username_format as follows. %u won’t drop away the domain. This allows users to login with the full email address.

auth_username_format = %u

Uncomment the following line at the end of this file, so Dovecot can query user information from the database.

!include auth-sql.conf.ext

If you don’t want local Unix users to send emails without registering email addresses in PostfixAdmin, then comment out the following line by adding the # character at the beginning, so Dovecot won’t query the local /etc/passwd or /etc/shadow file.

#!include auth-system.conf.ext

It can be helpful to add the following two lines in this file to debug login issues. The login errors would be logged into /var/log/mail.log file. (Once users can login without problems, you can comment out the following two lines.)

auth_debug = yes
auth_debug_passwords = yes

Edit the dovecot-sql.conf.ext file.

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

Here is the content that you should have. Replace password with the postfixadmin password you set in Step 1.

driver = mysql

connect = host=localhost dbname=postfixadmin user=postfixadmin password=password

default_pass_scheme = ARGON2I

password_query = SELECT username AS user,password FROM mailbox WHERE username = '%u' AND active='1'

user_query = SELECT maildir, 2000 AS uid, 2000 AS gid FROM mailbox WHERE username = '%u' AND active='1'

iterate_query = SELECT username AS user FROM mailbox

Restart Dovecot.

sudo systemctl restart dovecot

When a user tries to log in, Dovecot would use the Argon2 algorithm to generate a password hash from the password entered by the user, then compare it with the password hash stored in the database.

Step 10: Add Domain and Mailboxes in PostfixAdmin

Log in to PostfixAdmin web interface as the admin. Click the Domain List tab and select New Domain to add a domain. You can choose how many aliases and mailboxes are allowed for this domain.

Then click Virtual List tab and select Add Mailbox to add a new email address for your domain.

Next, you can open your desktop email client such as Mozilla Thunderbird and add a mail account.

• In the incoming server section, select IMAP protocol, enter mail.your-domain.com as the server name, choose port 143 and STARTTLS. Choose normal password as the authentication method.
• In the outgoing section, select SMTP protocol, enter mail.your-domain.com as the server name, choose port 587 and STARTTLS. Choose normal password as the authentication method.

You should now be able to connect to your own email server and also send and receive emails with your desktop email client! Note that you cannot use local Unix accounts to login now. You must log in with the virtual user created from PostfixAdmin web interface.

Troubleshooting Tips

If you can’t log into your mail server from a desktop mail client, scan your mail server to find if the ports are open. Note that you should run the following command from another Linux computer or server. If you run it on your mail server, then the ports will always appear to be open.

sudo nmap mail.example.com

And check if Dovecot is running.

systemctl status dovecot

You can also check the mail log (/var/log/mail.log), which may give you some clues.

Change User Password in PostfixAdmin

Users can log into PostfixAdmin at https://postfixadmin.example.com/users/login.php, then change their passwords.

Next Step

I hope this tutorial helped you install and use PostfixAdmin on Ubuntu 20.04 to create virtual mailboxes. In part 4, I will show you how to set up SPF and DKIM with Postfix to improve email deliverability and in a future tutorial, I’m going to show you how to host multiple domains with PostfixAdmin.

If you want to access emails from a web browser, then I recommend Roundcube, which is a very popular and featured-rich open-source webmail client. As always, if you found this post useful,  subscribe to our free newsletter to get more tips and tricks. Take care 🙂