How to Self-Host Postal — Open Source Email 2026

TL;DR

Postal is a full-featured, open source email sending platform — a direct alternative to Mailgun and SendGrid for applications that need transactional email via API or SMTP. It handles millions of emails, provides open/click tracking, bounce handling, spam filtering, webhooks, and a clean web dashboard. Self-hosting eliminates per-email fees: Mailgun charges $35/month for 50K emails; a Hetzner VPS running Postal handles 500K+ emails/month for ~€10/month. The catch: email deliverability requires careful DNS setup (DKIM, SPF, DMARC, rDNS) and a clean IP reputation.

Key Takeaways

• Postal: 14K+ GitHub stars, written in Ruby, production-grade since 2016, used by thousands of companies
• API + SMTP: sends via REST API or SMTP relay — drop-in replacement for Mailgun/SendGrid credentials
• Tracking: open tracking (pixel), click tracking (URL rewriting), bounce handling, spam complaints all built-in
• Multi-domain/multi-tenant: one Postal instance can host multiple organizations, servers, and sending domains
• Deliverability essentials: your server IP must have rDNS, each domain needs SPF + DKIM + DMARC — Postal helps configure all of these
• Alternatives: Listmonk (newsletters/bulk, not transactional), Stalwart (receives email too), Haraka (Node.js, more DIY)

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Why Self-Host Email Sending?

Mailgun, SendGrid, and Postmark are reliable but expensive at scale:

Provider	Price per 50K emails
Mailgun	$35/month
SendGrid	$19.95/month
Postmark	$50/month
Postal (self-hosted)	~€10/month (VPS)

Beyond cost, self-hosting gives you:

• IP control: your dedicated IP builds its own reputation over time
• No vendor lock-in: your sending infrastructure isn't subject to account suspensions or policy changes
• Custom tracking domains: all tracking links go through your own domain
• Audit logs: every sent/bounced/opened email stored in your database
• Webhook control: delivery events sent to your endpoints, not stored in a third-party system

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Prerequisites

• VPS: 2 vCPU / 4GB RAM minimum (dedicated IP address — critical for email)
• Dedicated IP: must not be on any blacklists (check mxtoolbox.com/blacklists)
• Domain: a sending domain you control (e.g., mail.example.com)
• Reverse DNS: your IP's rDNS must resolve to your sending domain (set via your VPS provider's control panel)
• Docker + Docker Compose: installed on the server
• Open ports: 25 (SMTP), 587 (submission), 443 (web)

Important: Many cloud providers block port 25 by default (AWS, GCP, Hetzner). Check before starting. Hetzner allows port 25 after a brief request form. AWS requires contacting support. DigitalOcean allows it by default on dedicated Droplets.

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Docker Compose Setup

Create /opt/postal/docker-compose.yml:

version: '3.8'

services:
  mariadb:
    image: mariadb:10.11
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: ${DB_ROOT_PASSWORD}
      MYSQL_DATABASE: postal
      MYSQL_USER: postal
      MYSQL_PASSWORD: ${DB_PASSWORD}
    volumes:
      - ./mariadb:/var/lib/mysql

  rabbitmq:
    image: rabbitmq:3.13-management-alpine
    restart: always
    environment:
      RABBITMQ_DEFAULT_USER: postal
      RABBITMQ_DEFAULT_PASS: ${RABBITMQ_PASSWORD}
    volumes:
      - ./rabbitmq:/var/lib/rabbitmq

  postal:
    image: ghcr.io/postalserver/postal:latest
    restart: always
    ports:
      - "25:25"
      - "127.0.0.1:5000:5000"  # web UI (proxy via nginx)
    volumes:
      - ./config:/config
    depends_on:
      - mariadb
      - rabbitmq
    command: postal run

  postal-worker:
    image: ghcr.io/postalserver/postal:latest
    restart: always
    volumes:
      - ./config:/config
    depends_on:
      - mariadb
      - rabbitmq
    command: postal worker

  postal-cron:
    image: ghcr.io/postalserver/postal:latest
    restart: always
    volumes:
      - ./config:/config
    depends_on:
      - mariadb
      - rabbitmq
    command: postal cron

---

Configuration File

Create /opt/postal/config/postal.yml:

version: 1

web_server:
  host: postal.example.com
  protocol: https
  port: 443

main_db:
  host: mariadb
  username: postal
  password: "${DB_PASSWORD}"
  database: postal

message_db:
  host: mariadb
  username: postal
  password: "${DB_PASSWORD}"
  prefix: postal

rabbitmq:
  host: rabbitmq
  username: postal
  password: "${RABBITMQ_PASSWORD}"
  vhost: /postal

smtp_server:
  port: 25
  tls_enabled: true
  tls_certificate_path: /config/smtp.crt
  tls_private_key_path: /config/smtp.key

dns:
  mx_records:
    - postal.example.com
  smtp_server_hostname: postal.example.com
  spf_include: spf.postal.example.com
  dkim_identifier: postal
  return_path: rp.postal.example.com
  route_domain: routes.postal.example.com

logging:
  rails_log_enabled: true

Create .env:

DB_ROOT_PASSWORD=strong-root-password
DB_PASSWORD=strong-postal-password
RABBITMQ_PASSWORD=strong-rabbit-password

---

Initial Setup

# Initialize the database and create admin user
docker compose run --rm postal postal initialize
# Prompts for admin email and password

# Start all services
docker compose up -d

# Generate DKIM keys for your first domain (run after setup)
docker compose exec postal postal generate-dkim postal.example.com

---

DNS Configuration

Postal generates exact DNS records after setup. Configure these in your DNS provider:

Required records for example.com sending domain:

; SPF — authorizes Postal's IP to send for example.com
example.com.   TXT   "v=spf1 include:spf.postal.example.com ~all"

; DKIM — cryptographic signature (copy from Postal dashboard)
postal._domainkey.example.com.   TXT   "v=DKIM1; k=rsa; p=MIGfMA0GCS..."

; DMARC — policy for SPF/DKIM failures
_dmarc.example.com.   TXT   "v=DMARC1; p=quarantine; rua=mailto:dmarc@example.com"

; Return path (bounces)
rp.example.com.   CNAME   rp.postal.example.com.

; Postal server MX (for receiving bounces)
postal.example.com.   MX 10   postal.example.com.
postal.example.com.   A       <your-server-ip>

Reverse DNS: In your VPS control panel, set the rDNS (PTR record) for your server IP to postal.example.com. This is mandatory — major email providers reject connections from IPs without matching rDNS.

---

Sending via API

Postal provides a simple HTTP API compatible with most email libraries:

// Send via Postal API
const response = await fetch('https://postal.example.com/api/v1/send/message', {
  method: 'POST',
  headers: {
    'X-Server-API-Key': 'your-api-key-from-postal-dashboard',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    to: ['user@example.com'],
    from: 'noreply@yourdomain.com',
    subject: 'Welcome to our app!',
    html_body: '<h1>Welcome!</h1><p>Thanks for signing up.</p>',
    text_body: 'Welcome! Thanks for signing up.',
    reply_to: 'support@yourdomain.com',
    headers: {
      'X-Custom-Header': 'value',
    },
  }),
})

const result = await response.json()
// result.data.messages['user@example.com'].id — message ID for tracking

---

Sending via SMTP

For existing apps that use SMTP, configure Postal as your SMTP server:

SMTP_HOST=postal.example.com
SMTP_PORT=587
SMTP_USER=<credential-key-from-postal-dashboard>
SMTP_PASS=<credential-secret>
SMTP_FROM=noreply@yourdomain.com

This works as a drop-in replacement for Mailgun, SendGrid, or SES SMTP credentials — change the host/user/pass and you're done.

---

Webhooks for Delivery Events

Configure webhooks in the Postal dashboard → HTTP Endpoints:

// app/api/postal-webhook/route.ts
export async function POST(req: Request) {
  const body = await req.json()

  switch (body.event) {
    case 'MessageDelivered':
      await markEmailDelivered(body.payload.message.id)
      break
    case 'MessageBounced':
      await handleBounce(body.payload.message.to, body.payload.bounce.type)
      break
    case 'MessageLinkClicked':
      await recordClick(body.payload.message.id, body.payload.url)
      break
    case 'MessageOpened':
      await recordOpen(body.payload.message.id)
      break
    case 'SpamComplaint':
      await unsubscribeUser(body.payload.message.to)
      break
  }

  return new Response('OK')
}

Postal signs webhooks with an HMAC-SHA256 signature — verify it in production:

import { createHmac } from 'crypto'

function verifyPostalSignature(payload: string, signature: string, secret: string): boolean {
  const expected = createHmac('sha256', secret).update(payload).digest('hex')
  return signature === expected
}

---

Rate Limiting and Queue Management

Postal processes email delivery via RabbitMQ queues. Configure sending limits to protect your IP reputation and prevent being blacklisted:

In the Postal web dashboard → Servers → your server → Settings:

• Send limit: max emails per hour (start at 200/hr, increase as reputation builds)
• Send limit period: the window for the send limit (1 hour recommended)
• Bounce rate threshold: auto-suspend sending if bounce rate exceeds X% (5% is a safe threshold)

For high-volume sends, spread sending over time rather than blasting all at once:

// Stagger bulk sends with Sidekiq/BullMQ
async function sendCampaignEmail(recipients: string[], templateId: string) {
  const BATCH_SIZE = 100
  const DELAY_MS = 10_000  // 10 seconds between batches

  for (let i = 0; i < recipients.length; i += BATCH_SIZE) {
    const batch = recipients.slice(i, i + BATCH_SIZE)
    await Promise.all(batch.map(email => sendViaPostal(email, templateId)))

    if (i + BATCH_SIZE < recipients.length) {
      await new Promise(resolve => setTimeout(resolve, DELAY_MS))
    }
  }
}

---

Monitoring Postal

Check Postal's health via its built-in dashboard:

1. Messages dashboard: real-time view of queued, held, delivered, bounced, and failed messages
2. SMTP logs: raw SMTP conversation logs for every delivery attempt
3. Suppression list: addresses Postal has auto-suppressed due to hard bounces or spam complaints

Set up external monitoring with Uptime Kuma or similar:

# Uptime Kuma monitor for Postal web
- name: Postal Web UI
  url: https://postal.example.com
  type: http
  interval: 60

# TCP monitor for SMTP port
- name: Postal SMTP Port 25
  host: postal.example.com
  port: 25
  type: tcp
  interval: 60

For metrics, Postal exposes a /metrics endpoint compatible with Prometheus:

# prometheus.yml scrape config
scrape_configs:
  - job_name: postal
    static_configs:
      - targets: ['postal.example.com:5000']
    metrics_path: /metrics
    bearer_token: your-postal-api-key

---

Troubleshooting Common Issues

Emails landing in spam:

• Run your domain through mail-tester.com to get a spam score and specific recommendations
• Check that DKIM signature is valid: dig +short postal._domainkey.yourdomain.com TXT
• Verify DMARC policy isn't blocking legitimate sends: check Google Postmaster Tools for delivery rate
• Ensure your server IP isn't on any blacklists: mxtoolbox.com/blacklists

Port 25 connection refused:

# Test if port 25 is accessible from outside
nmap -p 25 postal.example.com
# If filtered: check VPS firewall and provider port 25 policy
ufw allow 25/tcp

High bounce rate causing auto-suspension:

# Check bounce types in Postal dashboard
# Hard bounces (invalid address) — remove from your list permanently
# Soft bounces (mailbox full, temp failures) — retry after 24h
# Reset suspension after fixing the root cause
docker compose exec postal postal unsuspend-server <server-id>

RabbitMQ queue backup:

# Check queue depths via management UI at :15672
# Or via CLI:
docker compose exec rabbitmq rabbitmqctl list_queues name messages
# If postal.delivery queue is backing up, restart workers:
docker compose restart postal-worker

---

Deliverability Best Practices

1. Warm up your IP: Don't blast 10,000 emails on day one. Start with 50-100/day and ramp up over 2-4 weeks
2. Monitor blacklists: check mxtoolbox.com/blacklists weekly for the first month
3. Handle bounces: Postal auto-disables addresses after hard bounces — honor this in your app
4. Respect unsubscribes: process SpamComplaint webhooks immediately
5. Use consistent From address: changing from addresses hurts reputation
6. Send relevant content: low engagement → spam folders → reputation damage

---

Backup and Upgrades

Daily backup script:

#!/bin/bash
DATE=$(date +%Y%m%d)
BACKUP_DIR=/opt/backups/postal

mkdir -p $BACKUP_DIR

# Dump both postal databases
docker compose exec -T mariadb mysqldump -u root -p${DB_ROOT_PASSWORD} postal > "$BACKUP_DIR/postal-$DATE.sql"
docker compose exec -T mariadb mysqldump -u root -p${DB_ROOT_PASSWORD} --databases $(docker compose exec -T mariadb mysql -u root -p${DB_ROOT_PASSWORD} -e "SHOW DATABASES LIKE 'postal-msg-%';" --skip-column-names | tr '\n' ' ') > "$BACKUP_DIR/postal-msg-$DATE.sql"

gzip "$BACKUP_DIR/postal-$DATE.sql"
gzip "$BACKUP_DIR/postal-msg-$DATE.sql"

# Keep 14 days
find $BACKUP_DIR -name "*.gz" -mtime +14 -delete

Note: Postal creates a separate database per mail server (named postal-msg-<id>). Back up all of them.

Upgrading Postal:

cd /opt/postal
# Pull latest image
docker compose pull postal postal-worker postal-cron

# Run any pending database migrations
docker compose run --rm postal postal upgrade

# Restart all Postal services
docker compose up -d --force-recreate postal postal-worker postal-cron

Always check the Postal changelog before upgrading. Major releases sometimes require manual migration steps for database schema changes.

---

Methodology

• Postal documentation: docs.postalserver.io
• GitHub: github.com/postalserver/postal (14K+ stars)
• Tested with Postal 3.x, Docker Compose, MariaDB 10.11, on Hetzner CX22

Why Self-Host Postal — Open Source Email?

The case for self-hosting Postal — Open Source Email comes down to three practical factors: data ownership, cost at scale, and operational control.

Data ownership is the fundamental argument. When you use a SaaS version of any tool, your data lives on someone else's infrastructure subject to their terms of service, their security practices, and their business continuity. If the vendor raises prices, gets acquired, changes API limits, or shuts down, you're left scrambling. Self-hosting Postal — Open Source Email means your data and configuration stay on infrastructure you control — whether that's a VPS, a bare metal server, or a home lab.

Cost at scale matters once you move beyond individual use. Most SaaS equivalents charge per user or per data volume. A self-hosted instance on a $10-20/month VPS typically costs less than per-user SaaS pricing for teams of five or more — and the cost doesn't scale linearly with usage. One well-configured server handles dozens of users for a flat monthly fee.

Operational control is the third factor. The Docker Compose configuration above exposes every setting that commercial equivalents often hide behind enterprise plans: custom networking, environment variables, storage backends, and authentication integrations. You decide when to update, how to configure backups, and what access controls to apply.

The honest tradeoff: you're responsible for updates, backups, and availability. For teams running any production workloads, this is familiar territory. For individuals, the learning curve is real but the tooling (Docker, Caddy, automated backups) is well-documented and widely supported.

Server Requirements and Sizing

Before deploying Postal — Open Source Email, assess your server capacity against expected workload.

Minimum viable setup: A 1 vCPU, 1GB RAM VPS with 20GB SSD is sufficient for personal use or small teams. Most consumer VPS providers — Hetzner, DigitalOcean, Linode, Vultr — offer machines in this range for $5-10/month. Hetzner offers excellent price-to-performance for European and US regions.

Recommended production setup: 2 vCPUs with 4GB RAM and 40GB SSD handles most medium deployments without resource contention. This gives Postal — Open Source Email headroom for background tasks, caching, and concurrent users while leaving capacity for other services on the same host.

Storage planning: The Docker volumes in this docker-compose.yml store all persistent Postal — Open Source Email data. Estimate your storage growth rate early — for data-intensive tools, budget for 3-5x your initial estimate. Hetzner Cloud and Vultr both support online volume resizing without stopping your instance.

Operating system: Any modern 64-bit Linux distribution works. Ubuntu 22.04 LTS and Debian 12 are the most commonly tested configurations. Ensure Docker Engine 24.0+ and Docker Compose v2 are installed — verify with docker --version and docker compose version. Avoid Docker Desktop on production Linux servers; it adds virtualization overhead and behaves differently from Docker Engine in ways that cause subtle networking issues.

Network: Only ports 80 and 443 need to be publicly accessible when running behind a reverse proxy. Internal service ports should be bound to localhost only. A minimal UFW firewall that blocks all inbound traffic except SSH, HTTP, and HTTPS is the single most effective security measure for a self-hosted server.

Backup and Disaster Recovery

Running Postal — Open Source Email without a tested backup strategy is an unacceptable availability risk. Docker volumes are not automatically backed up — if you delete a volume or the host fails, data is gone with no recovery path.

What to back up: The named Docker volumes containing Postal — Open Source Email's data (database files, user uploads, application state), your docker-compose.yml and any customized configuration files, and .env files containing secrets.

Backup approach: For simple setups, stop the container, archive the volume contents, then restart. For production environments where stopping causes disruption, use filesystem snapshots or database dump commands (PostgreSQL pg_dump, SQLite .backup, MySQL mysqldump) that produce consistent backups without downtime.

For a complete automated backup workflow that ships snapshots to S3-compatible object storage, see the Restic + Rclone backup guide. Restic handles deduplication and encryption; Rclone handles multi-destination uploads. The same setup works for any Docker volume.

Backup cadence: Daily backups to remote storage are a reasonable baseline for actively used tools. Use a 30-day retention window minimum — long enough to recover from mistakes discovered weeks later. For critical data, extend to 90 days and use a secondary destination.

Restore testing: A backup that has never been restored is a backup you cannot trust. Once a month, restore your Postal — Open Source Email backup to a separate Docker Compose stack on different ports and verify the data is intact. This catches silent backup failures, script errors, and volume permission issues before they matter in a real recovery.

Security Hardening

Self-hosting means you are responsible for Postal — Open Source Email's security posture. The Docker Compose setup provides a functional base; production deployments need additional hardening.

Always use a reverse proxy: Never expose Postal — Open Source Email's internal port directly to the internet. The docker-compose.yml binds to localhost; Caddy or Nginx provides HTTPS termination. Direct HTTP access transmits credentials in plaintext. A reverse proxy also centralizes TLS management, rate limiting, and access logging.

Strong credentials: Change default passwords immediately after first login. For secrets in docker-compose environment variables, generate random values with openssl rand -base64 32 rather than reusing existing passwords.

Firewall configuration:

ufw default deny incoming
ufw allow 22/tcp
ufw allow 80/tcp
ufw allow 443/tcp
ufw enable

Internal service ports (databases, admin panels, internal APIs) should only be reachable from localhost or the Docker network, never directly from the internet.

Network isolation: Docker Compose named networks keep Postal — Open Source Email's services isolated from other containers on the same host. Database containers should not share networks with containers that don't need direct database access.

VPN access for sensitive services: For internal-only tools, restricting access to a VPN adds a strong second layer. Headscale is an open source Tailscale control server that puts your self-hosted stack behind a WireGuard mesh, eliminating public internet exposure for internal tools.

Update discipline: Subscribe to Postal — Open Source Email's GitHub releases page to receive security advisory notifications. Schedule a monthly maintenance window to pull updated images. Running outdated container images is the most common cause of self-hosted service compromises.

Troubleshooting Common Issues

Container exits immediately or won't start

Check logs first — they almost always explain the failure:

docker compose logs -f postal

Common causes: a missing required environment variable, a port already in use, or a volume permission error. Port conflicts appear as bind: address already in use. Find the conflicting process with ss -tlpn | grep PORT and either stop it or change Postal — Open Source Email's port mapping in docker-compose.yml.

Cannot reach the web interface

Work through this checklist:

1. Confirm the container is running: docker compose ps
2. Test locally on the server: curl -I http://localhost:PORT
3. If local access works but external doesn't, check your firewall: ufw status
4. If using a reverse proxy, verify it's running and the config is valid: caddy validate --config /etc/caddy/Caddyfile

Permission errors on volume mounts

Some containers run as a non-root user. If the Docker volume is owned by root, the container process cannot write to it. Find the volume's host path with docker volume inspect VOLUME_NAME, check the tool's documentation for its expected UID, and apply correct ownership:

chown -R 1000:1000 /var/lib/docker/volumes/your_volume/_data

High resource usage over time

Memory or CPU growing continuously usually indicates unconfigured log rotation, an unbound cache, or accumulated data needing pruning. Check current usage with docker stats postal. Add resource limits in docker-compose.yml to prevent one container from starving others. For ongoing visibility into resource trends, deploy Prometheus + Grafana or Netdata.

Data disappears after container restart

Data stored in the container's writable layer — rather than a named volume — is lost when the container is removed or recreated. This happens when the volume mount path in docker-compose.yml doesn't match where the application writes data. Verify mount paths against the tool's documentation and correct the mapping. Named volumes persist across container removal; only docker compose down -v deletes them.

Keeping Postal — Open Source Email Updated

Postal — Open Source Email follows a regular release cadence. Staying current matters for security patches and compatibility. The update process with Docker Compose is straightforward:

docker compose pull          # Download updated images
docker compose up -d         # Restart with new images
docker image prune -f        # Remove old image layers (optional)

Read the changelog before major version updates. Some releases include database migrations or breaking configuration changes. For major version bumps, test in a staging environment first — run a copy of the service on different ports with the same volume data to validate the migration before touching production.

Version pinning: For stability, pin to a specific image tag in docker-compose.yml instead of latest. Update deliberately after reviewing the changelog. This trades automatic patch delivery for predictable behavior — the right call for business-critical services.

Post-update verification: After updating, confirm Postal — Open Source Email is functioning correctly. Most services expose a /health endpoint that returns HTTP 200 — curl it from the server or monitor it with your uptime tool.

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Browse open source alternatives to email marketing and transactional email tools on OSSAlt.

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