High Availability Mail Server Setup (Postfix + HAProxy + Replication) on Ubuntu 22.04

Introduction

In production, one single mail server is risky.
If it fails, all email services go down.
To avoid downtime, companies use High Availability (HA) setups.
In this guide, we will build a HA mail system using Postfix, Dovecot, HAProxy, and Replication on Ubuntu 22.04.

Architecture Overview

• Two Postfix + Dovecot servers → handle mail processing and store user mailboxes.
• One HAProxy server → load balances requests between mail servers.
• Replication → keeps mailboxes identical across both servers.
• DNS MX records → point to HAProxy for high availability.

Mail flow: User → HAProxy → Mail Server 1 or Mail Server 2.

Step 1: Prepare Servers

We need:

• 2 x Mail Servers (Postfix + Dovecot) → mail1.bitscentric.local, mail2.bitscentric.local
• 1 x HAProxy Load Balancer → haproxy.bitscentric.local

Step 2: Install Postfix + Dovecot on Mail Servers

Run on both mail1 and mail2:

sudo apt update
sudo apt install -y postfix dovecot-core dovecot-imapd dovecot-pop3d

Configure Postfix (/etc/postfix/main.cf):

myhostname = mail1.bitscentric.local   # change on mail2 to mail2.bitscentric.local
mydomain = bitscentric.local
myorigin = $mydomain
home_mailbox = Maildir/
inet_interfaces = all

Configure Dovecot (/etc/dovecot/conf.d/10-mail.conf):

mail_location = maildir:~/Maildir

Step 3: Setup Mailbox Replication

We will use Dovecot dsync (recommended) or rsync to replicate mailboxes.

Edit Dovecot config (/etc/dovecot/conf.d/10-master.conf):

service replicator {
  unix_listener replicator-doveadm {
    user = dovecot
  }
}

Enable dsync replication (run on both servers):

doveadm sync -u user1@bitscentric.local tcp:mail2.bitscentric.local

Set up cron job for automatic sync:

*/5 * * * * doveadm sync -A tcp:mail2.bitscentric.local

Step 4: Install HAProxy on Load Balancer

sudo apt update
sudo apt install -y haproxy

Edit HAProxy config (/etc/haproxy/haproxy.cfg):

frontend smtp_frontend
    bind *:25
    mode tcp
    default_backend smtp_backend

backend smtp_backend
    mode tcp
    balance roundrobin
    server mail1 mail1.bitscentric.local:25 check
    server mail2 mail2.bitscentric.local:25 check

frontend imap_frontend
    bind *:143
    mode tcp
    default_backend imap_backend

backend imap_backend
    mode tcp
    balance roundrobin
    server mail1 mail1.bitscentric.local:143 check
    server mail2 mail2.bitscentric.local:143 check

frontend imaps_frontend
    bind *:993
    mode tcp
    default_backend imaps_backend

backend imaps_backend
    mode tcp
    balance roundrobin
    server mail1 mail1.bitscentric.local:993 check
    server mail2 mail2.bitscentric.local:993 check

Step 5: Restart Services

On mail servers:

sudo systemctl restart postfix dovecot

On HAProxy server:

sudo systemctl restart haproxy

Step 6: Configure DNS

Set MX record for domain bitscentric.local to point to HAProxy:

bitscentric.local.   IN   MX   10   haproxy.bitscentric.local.

Step 7: Testing High Availability

• Send email to user1@bitscentric.local.
• HAProxy will forward request to mail1 or mail2.
• Stop mail1 → mail2 still handles requests.
• Mailboxes stay in sync using dsync.

Benefits of High Availability Mail Server

• No single point of failure – if one server fails, another works.
• Better performance – HAProxy balances the load.
• Mailbox replication – user mails are safe and available on both servers.
• Scalability – easy to add more mail servers.
• Production ready – enterprise-level design.

Best Practices

• Use SSL/TLS on Postfix, Dovecot, and HAProxy for secure communication.
• Implement SPF, DKIM, DMARC DNS records for email delivery.
• Monitor logs (/var/log/mail.log and /var/log/haproxy.log).
• Set up backups for mailbox store and MySQL database.
• Test failover regularly by shutting down one mail server.

Conclusion

We have successfully built a High Availability mail server setup with Postfix + Dovecot + HAProxy + Replication on Ubuntu 22.04.
This design ensures emails are always available, load is balanced, and no single failure can stop your mail service.
This is the kind of setup used in real-world companies for production mail servers.