Postal mail server: a self-hosted SendGrid alternative on your VPS
Postal is an open-source mail server for transactional email, effectively a self-hosted SendGrid alternative (or Mailgun alternative, or Postmark alternative). Run it on your VPS for password resets, order confirmations, signup verifications, invoice notifications, and any other application email without paying per-message fees.
The difference from hosted services: you run the Postal mail server on your own server and you don’t pay per message. Whether you send 100 emails a month or 100,000, your only cost is the VPS itself.
Why self-host a mail server
Hosted email services charge by volume. Fine for small traffic, expensive as you grow. SendGrid’s free tier caps at 100 emails per day. Past that, you’re paying per thousand messages, and it adds up.
With Postal on your own VPS, you control everything:
- No per-message fees. Send as much as your server can handle.
- Your data stays yours. Email content, recipient lists, delivery logs never touch a third party.
- Full control over sending reputation. You manage your own IP instead of sharing one with thousands of other senders.
- No sudden account suspensions. SaaS email providers sometimes flag legitimate senders and suspend accounts without warning. Your server, your rules.
What the Postal mail server gives you
Postal isn’t just a basic SMTP relay. It’s a full platform:
- Web UI for managing organizations, servers, and credentials
- HTTP API and SMTP for sending from your applications
- Click and open tracking to know if people actually read your emails
- Webhook support for delivery notifications, bounces, and complaints
- Multiple organizations and mail servers from one installation
- Searchable message logs for debugging delivery issues
- IP pool management for separating different traffic types
VPS requirements for a Postal mail server
Postal needs a bit more than the smallest VPS plan:
| Component | Minimum | Recommended |
|---|---|---|
| RAM | 4 GB | 8 GB |
| vCPUs | 2 | 4 |
| Storage | 20 GB | 50 GB+ |
| OS | Ubuntu 22.04/24.04 | Ubuntu 24.04 |
You also need:
- A domain you control (for DNS records)
- A clean IP address (fresh ColossusCloud VPS IPs work well)
- Reverse DNS (PTR record) set up for your VPS IP
Installing Postal on your VPS
Postal uses Docker. The flow:
- Deploy an Ubuntu VPS with at least 4 GB RAM
- Install Docker and Docker Compose
- Clone the Postal installation helper repository
- Run the setup script to initialize the database and create your admin user
- Configure DNS records (MX, SPF, DKIM, DMARC) for your sending domain
- Set up a reverse proxy with Nginx and SSL via Certbot
- Log into the web UI and create your first mail server
The Postal documentation walks through each step. The whole process takes 30-45 minutes if you’re comfortable with Linux and DNS.
DNS is the part that matters
This is where most self-hosted email setups fail. Sending email is easy. Getting it delivered to inboxes instead of spam folders is the hard part.
You’ll need:
- SPF record telling receiving servers that your VPS IP is allowed to send for your domain
- DKIM keys so receivers can verify messages haven’t been tampered with
- DMARC policy telling receivers what to do with messages that fail SPF/DKIM
- Reverse DNS (PTR record) matching your VPS IP to your sending domain
ColossusCloud lets you set reverse DNS through the Client Portal. The rest you configure at your DNS provider.
Getting these right is the difference between inbox and spam. See our email deliverability guide for the full setup.
When Postal beats a SendGrid-alternative SaaS
Postal makes sense when:
- You’re sending more than a few thousand transactional emails per month
- You want full control over sending infrastructure
- You care about email privacy and data sovereignty
- You’re comfortable managing a Linux server
If you’re sending a handful of emails, a paid service with a free tier might be simpler. Past the free tier, self-hosting with Postal saves real money every month.
Deliverability tips
Running your own mail server comes with responsibility:
- Warm up your IP slowly. Don’t send 50,000 emails on day one from a fresh IP. Start small, increase gradually over weeks.
- Monitor blacklists. Check your IP against major blacklists regularly. MXToolbox makes this easy.
- Handle bounces properly. Remove invalid addresses. High bounce rates hurt reputation.
- Use a dedicated VPS. Don’t run Postal on the same server as your web app. Keep email infrastructure separate.
Picking a data center for Postal
Email delivery speed depends partly on where your server sits relative to receiving mail servers. For US recipients, Ashburn or Dallas are solid. For European recipients, Amsterdam puts you close to major European mail infrastructure.
Ready to own your email infrastructure? Deploy a Linux VPS and set up the Postal mail server. For DNS configuration help, see our guides on SPF, DKIM, and DMARC and email deliverability.