How to Install Postal SMTP Server and Configure DNS (SPF, DKIM, DMARC)

Postal is a powerful open-source email platform that allows you to manage your own SMTP server for sending transactional and bulk emails. It provides a web interface, API, and SMTP access similar to services like SendGrid or Mailgun.

This guide shows how to install Postal on a VPS server using Docker, as well as how to configure DNS records for proper email delivery.

Minimum system requirements

• Ubuntu 22.04 server
• Minimum 4 GB RAM
• 2 CPU cores
• Public IP address
• Domain with DNS access

Step 1 – Prepare the server

ssh root@SERVER_IP

apt update && apt upgrade -y

apt install git curl jq -y

Step 2 – Install Docker

curl -fsSL https://get.docker.com | sh

docker --version

Postal runs entirely on Docker and cannot be used without it.

Step 3 – Configure Hostname, A record and Reverse DNS (PTR)

Correct hostname and DNS configuration is essential for email delivery and SSL issuance.

Set hostname

hostnamectl set-hostname postal.example.com

Edit hosts file:

nano /etc/hosts

127.0.0.1 localhost
SERVER_IP postal.example.com postal

Configure A record

postal.example.com → SERVER_IP

Configure PTR (Reverse DNS)

SERVER_IP → postal.example.com

Important: Hostname, A record and PTR must match exactly.

Step 4 – Install Postal helper

git clone https://github.com/postalserver/install /opt/postal/install
ln -s /opt/postal/install/bin/postal /usr/bin/postal

Step 5 – Start MariaDB (Docker)

docker run -d \
   --name postal-mariadb \
   -p 127.0.0.1:3306:3306 \
   --restart always \
   -e MARIADB_DATABASE=postal \
   -e MARIADB_ROOT_PASSWORD=StrongPassword \
   mariadb

Step 6 – Generate configuration

postal bootstrap postal.example.com

Step 7 – Configure Postal

nano /opt/postal/config/postal.yml

main_db:
  host: 127.0.0.1
  username: root
  password: StrongPassword
  database: postal

Step 8 – Initialize Postal

postal initialize

postal make-user

Step 9 – Start Postal

postal start

postal status

Step 10 – Start Caddy (Docker)

docker run -d \
   --name postal-caddy \
   --restart always \
   --network host \
   -v /opt/postal/config/Caddyfile:/etc/caddy/Caddyfile \
   -v /opt/postal/caddy-data:/data \
   caddy

Step 11 – DNS configuration

MX record

postal.example.com → postal.example.com

SPF record

v=spf1 ip4:SERVER_IP ~all

DKIM record

Will be generated in the Postal interface.

Return-Path domain

rp.postal.example.com → SERVER_IP

Step 12 – Access Postal

https://postal.example.com

Step 13 – Create SMTP server

1. Create Organization
2. Create Mail Server
3. Add domain
4. Generate SMTP credentials

Example SMTP configuration

SMTP Host: postal.example.com
SMTP Port: 587
Encryption: TLS
Username: your_username
Password: your_password

Step 14 – Upgrade Postal

cd /opt/postal/install
git pull
postal update
postal restart

Conclusion

Postal runs entirely on Docker and uses containers for MariaDB and Caddy. With proper DNS configuration and correct hostname setup, you can achieve reliable email delivery.