How to Create a Local Mail Server for Testing Without Public DNS

This tutorial explains how to create a complete local mail server using Postfix, Dovecot, and MariaDB. The server can be tested locally without configuring public DNS records or receiving email from the Internet.

What We Are Building

The mail server consists of three main components:

Postfix

Postfix is the Mail Transfer Agent, or MTA. It:

• receives email;
• sends email;
• determines where messages should be delivered;
• delivers messages to local virtual mailboxes.

Postfix does not provide IMAP access and does not let users read their mail directly.

Dovecot

Dovecot:

• authenticates mailbox users;
• provides access through IMAP;
• reads and manages messages stored in Maildir format.

Dovecot does not normally receive email directly from other Internet mail servers.

MariaDB

Instead of creating one Linux account for every mailbox, we will store domains, mailbox users, password hashes, and aliases in a MariaDB database.

For example:

Email address	Password
email@myDomain.com	Secure password hash

1. Install MariaDB

sudo apt update
sudo apt install mariadb-server mariadb-client -y
sudo reboot

After the server restarts, verify the MariaDB installation:

mariadb --version
sudo systemctl status mariadb

2. Create the Mail Database

Open the MariaDB administration console:

sudo mysql

Create the database:

CREATE DATABASE mailserver
CHARACTER SET utf8mb4
COLLATE utf8mb4_unicode_ci;

SHOW DATABASES;

USE mailserver;

Create the virtual_domains table

CREATE TABLE virtual_domains (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255) NOT NULL UNIQUE
);

Create the virtual_users table

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

Create the virtual_aliases table

CREATE TABLE virtual_aliases (
    id INT AUTO_INCREMENT PRIMARY KEY,
    domain_id INT NOT NULL,
    source VARCHAR(255) NOT NULL,
    destination VARCHAR(255) NOT NULL,
    FOREIGN KEY (domain_id)
        REFERENCES virtual_domains(id)
        ON DELETE CASCADE
);

3. Create a Restricted Database User

Postfix and Dovecot should not connect to MariaDB using its root account. Create a dedicated account that has read-only access to the mail database.

CREATE USER 'mailuser'@'localhost'
IDENTIFIED BY 'YOUR_STRONG_PASSWORD';

GRANT SELECT ON mailserver.*
TO 'mailuser'@'localhost';

FLUSH PRIVILEGES;

If you made a mistake use:

ALTER USER 'mailuser'@'localhost'
IDENTIFIED BY 'YOUR_STRONG_PASSWORD';

4. Verify the Database

USE mailserver;
SHOW TABLES;

The result should contain the following tables:

+----------------------+
| Tables_in_mailserver |
+----------------------+
| virtual_aliases      |
| virtual_domains      |
| virtual_users        |
+----------------------+

Inspect the table structures:

DESCRIBE virtual_domains;
DESCRIBE virtual_users;
DESCRIBE virtual_aliases;

Verify that the restricted database user exists:

SELECT User, Host
FROM mysql.user
WHERE User = 'mailuser';

Verify its permissions:

SHOW GRANTS FOR 'mailuser'@'localhost';

The account should have SELECT permission on the mailserver database.

5. Add the First Virtual Domain

Open MariaDB if you previously closed it:

sudo mysql

Add the domain:

USE mailserver;

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

SELECT * FROM virtual_domains;

Public DNS is not required for local mailbox delivery. The domain is being used as a virtual mail domain inside Postfix and Dovecot.

6. Create the Virtual Mail User

All virtual mailboxes will be owned by one dedicated Linux user named vmail.

sudo groupadd -g 5000 vmail

sudo useradd \
    -g vmail \
    -u 5000 \
    -d /var/mail \
    -m \
    -s /usr/sbin/nologin \
    vmail

Create the root directory for virtual mailboxes:

sudo mkdir -p /var/mail/vhosts
sudo chown -R vmail:vmail /var/mail/vhosts
sudo chmod 770 /var/mail/vhosts

Verify the directory and user:

ls -ld /var/mail/vhosts
id vmail

7. Generate the First Mailbox Password

Install the Dovecot core utilities:

sudo apt install -y dovecot-core

Generate an Argon2id password hash:

doveadm pw -s ARGON2ID

Dovecot will ask for the password twice and return a value similar to:

{ARGON2ID}$argon2id$v=19$m=65536,t=3,p=1$...

Copy the complete hash, including the {ARGON2ID} prefix. The database must contain the hash, not the plain-text mailbox password.

8. Insert the First Mailbox

Open MariaDB:

sudo mysql

Insert the mailbox:

USE mailserver;

INSERT INTO virtual_users
(
    domain_id,
    email,
    password,
    maildir
)
VALUES
(
    1,
    'email@myDomain.com',
    '<PASTE_HASH_HERE>',
    'myDomain.com/email/Maildir/'
);

Verify the mailbox:

SELECT id, email, maildir
FROM virtual_users;

Expected result:

+----+---------------------+-------------------------------+
| id | email               | maildir                       |
+----+---------------------+-------------------------------+
|  1 | email@myDomain.com  | myDomain.com/email/Maildir/   |
+----+---------------------+-------------------------------+

9. Install Dovecot

sudo apt install -y \
    dovecot-core \
    dovecot-imapd \
    dovecot-mysql

Verify the installed version:

dovecot --version

Check the service:

sudo systemctl status dovecot

10. Enable SQL Authentication in Dovecot

Open Dovecot's authentication configuration:

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

Find this line and comment it out:

#!include auth-system.conf.ext

Enable SQL authentication:

!include auth-sql.conf.ext

11. Configure Dovecot's SQL Connection

Open the SQL authentication file:

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

Replace its contents with:

sql_driver = mysql

mysql localhost {
  user = mailuser
  password = YOUR_STRONG_PASSWORD
  dbname = mailserver
}

passdb sql {
  default_password_scheme = ARGON2ID

  query = SELECT email AS user, password \
          FROM virtual_users \
          WHERE email = '%{user}'
}

userdb sql {
  query = SELECT \
          5000 AS uid, \
          5000 AS gid, \
          CONCAT(
              '/var/mail/vhosts/',
              SUBSTRING_INDEX(maildir, '/Maildir/', 1)
          ) AS home \
          FROM virtual_users \
          WHERE email = '%{user}'
}

Replace YOUR_STRONG_PASSWORD with the password belonging to the MariaDB account mailuser.

12. Configure Dovecot to Use Maildir

Open the mail configuration:

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

Set the following values:

mail_driver = maildir
mail_home = /var/mail/vhosts/%{user | domain}/%{user | username}
mail_path = ~/Maildir

Comment out or remove incompatible mbox settings:

# mail_inbox_path = /var/mail/%{user}
# mail_path = %{home}/mail

The resulting mailbox paths will follow this structure:

home      = /var/mail/vhosts/myDomain.com/email
mail_path = /var/mail/vhosts/myDomain.com/email/Maildir

Verify the active mail settings:

sudo doveconf -n | grep -E \
'mail_driver|mail_home|mail_path|mail_inbox_path'

13. Validate and Restart Dovecot

Always validate the configuration before restarting Dovecot:

sudo doveconf -n

When validation completes successfully, restart the service:

sudo systemctl restart dovecot
sudo systemctl status dovecot --no-pager

Test the password database

sudo doveadm auth test email@myDomain.com

Dovecot will ask for the mailbox password. A successful result should report that authentication succeeded.

Test the user database

sudo doveadm user email@myDomain.com

The result should contain values similar to:

uid=5000
gid=5000
home=/var/mail/vhosts/myDomain.com/email
mail=/var/mail/vhosts/myDomain.com/email/Maildir

14. Install Postfix

sudo apt install -y postfix postfix-mysql

During installation, select:

• General type of mail configuration: Internet Site
• System mail name: myDomain.com

Selecting Internet Site does not automatically expose the server to the Internet. Firewall rules, provider restrictions, port forwarding, and DNS still determine whether external systems can reach it.

15. Verify the Postfix Installation

Check the Postfix version:

postconf mail_version

Check the service:

sudo systemctl status postfix --no-pager

The service should report:

Active: active (running)

Verify MySQL support

postconf -m

The output should include:

mysql

If mysql is missing, verify that the postfix-mysql package was installed successfully.

16. Configure the Local Mail Hostname

Check the current hostname:

hostnamectl
hostname -f

The fully qualified hostname should be:

mail.myDomain.com

If necessary, set it:

sudo hostnamectl set-hostname mail.myDomain.com

Update /etc/hosts

Open the hosts file:

sudo nano /etc/hosts

Use a local entry similar to:

127.0.0.1 localhost
127.0.1.1 mail.myDomain.com mail

# The following lines are desirable for IPv6-capable hosts
::1 localhost ip6-localhost ip6-loopback

Verify the hostname again:

hostname
hostname -f

Both commands should identify the server as mail.myDomain.com.

17. Create the Postfix MariaDB Query Files

Postfix uses separate query files to look up virtual domains, mailboxes, and aliases. Each file has one specific responsibility.

Virtual domain lookup

sudo nano /etc/postfix/mysql-virtual-mailbox-domains.cf

user = mailuser
password = YOUR_MAILUSER_PASSWORD
hosts = localhost
dbname = mailserver
query = SELECT 1 FROM virtual_domains WHERE name='%s'

Virtual mailbox lookup

sudo nano /etc/postfix/mysql-virtual-mailbox-maps.cf

user = mailuser
password = YOUR_MAILUSER_PASSWORD
hosts = localhost
dbname = mailserver
query = SELECT maildir FROM virtual_users WHERE email='%s'

Virtual alias lookup

sudo nano /etc/postfix/mysql-virtual-alias-maps.cf

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

Replace YOUR_MAILUSER_PASSWORD in all three files with the password of the MariaDB account mailuser.

18. Secure the Postfix Query Files

These files contain a database password and must not be readable by every user.

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

Verify the permissions:

ls -l /etc/postfix/mysql-virtual-*.cf

Expected permissions:

-rw-r----- 1 root postfix ...

19. Test the Database Queries Before Configuring Postfix

Testing the individual lookup files before changing Postfix makes database, password, permission, and SQL errors much easier to identify.

Test the virtual domain

sudo postmap -q myDomain.com \
mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf

Expected result:

1

Test the mailbox

sudo postmap -q email@myDomain.com \
mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf

Expected result:

myDomain.com/email/Maildir/

Test the alias

sudo postmap -q email@myDomain.com \
mysql:/etc/postfix/mysql-virtual-alias-maps.cf

No output is expected when no alias exists for the address.

20. Configure Postfix for Virtual Mailboxes

First, inspect and save the current non-default settings:

postconf -n

Use postconf -e to change the configuration. This avoids duplicate parameters and reduces the possibility of syntax errors in /etc/postfix/main.cf.

sudo postconf -e \
"virtual_mailbox_domains=mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf"

sudo postconf -e \
"virtual_mailbox_maps=mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf"

sudo postconf -e \
"virtual_alias_maps=mysql:/etc/postfix/mysql-virtual-alias-maps.cf"

sudo postconf -e "virtual_mailbox_base=/var/mail/vhosts"
sudo postconf -e "virtual_uid_maps=static:5000"
sudo postconf -e "virtual_gid_maps=static:5000"
sudo postconf -e "virtual_transport=virtual"

21. Correct the mydestination Setting

Check the current value:

postconf mydestination

The virtual domain must not also be configured as a normal local destination. For example, this value would be incorrect:

mydestination = $myhostname, myDomain.com, ubuntu, localhost.localdomain, localhost

Set the appropriate value:

sudo postconf -e \
"mydestination=\$myhostname, localhost.\$mydomain, localhost"

Verify it:

postconf mydestination

Expected result:

mydestination = $myhostname, localhost.$mydomain, localhost

22. Validate and Restart Postfix

Validate the Postfix configuration:

sudo postfix check

My result: updating /etc/hosts => /var/spool/postfix//etc/hosts postfix/postfix-script: warning: not owned by root: /var/spool/postfix/etc/resolv.conf

Correct any errors before restarting the service. Some warnings may refer to files copied into Postfix's chroot environment. Review each warning carefully.

Restart Postfix:

sudo systemctl restart postfix
sudo systemctl status postfix --no-pager

23. Send a Local Test Message

Install the command-line mail client if it is not already available:

sudo apt install -y bsd-mailx

Send a message to the virtual mailbox:

printf "Hello from my first Postfix test.\n" \
| mail -s "First Mail" email@myDomain.com

Immediately inspect the Postfix log:

sudo journalctl -u postfix -n 50 --no-pager

Look for a successful delivery status. If delivery fails, the log normally indicates whether the problem involves permissions, a database lookup, an unknown mailbox, or an invalid path.

24. Verify That the Message Was Delivered

Search for files under the virtual mailbox directory:

sudo find /var/mail/vhosts -type f

You should see a message file similar to:

/var/mail/vhosts/myDomain.com/email/Maildir/new/1752910270.Vfd...

List the user's Dovecot mailboxes:

sudo doveadm mailbox list -u email@myDomain.com

A basic result should include:

INBOX

Finally, retrieve the subject from the inbox:

sudo doveadm fetch \
-u email@myDomain.com \
'hdr.subject' \
mailbox INBOX

Expected result:

hdr.subject: First Mail

Testing Without Public DNS

The local test works because Postfix recognizes myDomain.com as a virtual domain and delivers the message directly to the local Maildir. No public MX record is consulted during this local delivery.

When connecting from another computer on the same private network, add a temporary hosts-file entry on that computer:

192.168.1.50 mail.myDomain.com

Replace 192.168.1.50 with the private IP address of the mail server.

On Windows, edit this file as an administrator:

C:\Windows\System32\drivers\etc\hosts

On Linux, edit:

/etc/hosts

You can then configure an email client to connect to mail.myDomain.com without creating a public DNS record.

What Is Still Required for Internet Email?

A public production mail server normally also needs:

• a public A or AAAA record for the mail hostname;
• an MX record for the mail domain;
• reverse DNS configured by the hosting provider;
• SPF, DKIM, and DMARC records;
• a trusted TLS certificate;
• SMTP authentication for mail clients;
• submission ports such as 587 or 465;
• firewall rules for SMTP and IMAP ports;
• anti-spam and malware protection;
• a hosting provider that does not block outbound port 25.

Useful Diagnostic Commands

Check mail

sudo journalctl -u postfix | grep emailFromWhichIsSent@someDomain.com
sudo journalctl -u postfix --since "today" | grep emailFromWhichIsSent
find /var/mail/vhosts -type f | xargs grep -l "emailFromWhichIsSent@someDomain.com" 2>/dev/null
find /var/mail/vhosts -type f | xargs grep -l "Subject: test" 2>/dev/null
find /var/mail/vhosts -type f -printf "%TY-%Tm-%Td %TT %p\n" | sort

Test if anything is conected on port 25

sudo tcpdump -n -i any port 25

Test if DNS MX record is visible

dig @8.8.8.8 testmail.myDomain.com MX +short

Check services

sudo systemctl status mariadb --no-pager
sudo systemctl status dovecot --no-pager
sudo systemctl status postfix --no-pager

Validate configurations

sudo doveconf -n
sudo postfix check
postconf -n

Test the database lookups

sudo postmap -q myDomain.com \
mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf

sudo postmap -q email@myDomain.com \
mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf

Test Dovecot authentication

sudo doveadm auth test email@myDomain.com
sudo doveadm user email@myDomain.com

Inspect logs

sudo journalctl -u postfix -n 100 --no-pager
sudo journalctl -u dovecot -n 100 --no-pager
sudo journalctl -u mariadb -n 100 --no-pager

Inspect Maildir

sudo find /var/mail/vhosts -type f
sudo doveadm mailbox list -u email@myDomain.com
sudo doveadm fetch \
-u email@myDomain.com \
'hdr.subject' \
mailbox INBOX

Conclusion

We now have a functioning local mail server in which:

• MariaDB stores virtual domains, mailbox users, password hashes, and aliases;
• Postfix accepts and delivers messages to virtual Maildir mailboxes;
• Dovecot authenticates users and reads messages from Maildir;
• local delivery works without public DNS records.

This environment is suitable for learning, development, and application testing. It provides a good foundation for adding authenticated SMTP submission, TLS, public DNS, and external mail delivery later.