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3 open source alternatives to Mailgun

Developer-focused transactional email and SMTP relay. Here are the open source projects real teams use instead — ranked by fit, with honest pros and cons for each.

What people don't love about Mailgun

  • Deliverability varies heavily by region and plan.
  • Validation and inbound parsing are separate paid add-ons.
  • Log retention is limited on lower tiers.

Current Mailgun pricing (for reference): Flex pay-as-you-go from $0.80/1000 emails; Foundation from $15/month.

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Quick comparison

Alternative Best for License Self-host Hosted cloud?
Postal
Self-hosted mail server for sending transactional and bulk email. 		A batteries-included self-hosted replacement for the Mailgun SMTP relay. MIT ★★★★☆ Self-host only
Haraka
High-performance Node.js SMTP server used by big senders. 		Scriptable SMTP on Node.js for teams that want a custom mail pipeline. MIT ★★★★☆ Self-host only
Mautic
Open source marketing automation platform. 		When you need marketing automation on top of transactional sending. GPL-3.0 ★★★★☆ Yes

1. Postal — A batteries-included self-hosted replacement for the Mailgun SMTP relay.

Self-hosted mail server for sending transactional and bulk email.

Strengths

  • Web UI, SMTP and HTTP API out of the box.
  • Per-server tracking (opens, clicks, bounces).
  • Modular MariaDB + RabbitMQ architecture.

Weaknesses

  • Running a real mail server is a deliverability project, not an install.
  • IP warm-up and SPF/DKIM/DMARC on you.
  • Many cloud providers block outbound :25 entirely.
License: MIT Self-host difficulty: 4/5

Postal homepage · Source on GitHub · Mailgun vs Postal →

2. Haraka — Scriptable SMTP on Node.js for teams that want a custom mail pipeline.

High-performance Node.js SMTP server used by big senders.

Strengths

  • Plugin-based — you shape the flow in JavaScript.
  • Async core handles high connection counts.
  • Runs outbound relay and inbound MX workloads.

Weaknesses

  • Not a batteries-included product — you build on top.
  • Documentation assumes SMTP fluency.
  • No baked-in UI for campaign management.
License: MIT Self-host difficulty: 4/5

Haraka homepage · Source on GitHub · Mailgun vs Haraka →

3. Mautic — When you need marketing automation on top of transactional sending.

Open source marketing automation platform.

Strengths

  • Full marketing automation — campaigns, landing pages, scoring.
  • Large ecosystem.
  • Strong for B2B lead nurturing.

Weaknesses

  • Heavy self-host setup (PHP + queue + cron).
  • UI is complex and has a learning curve.
  • Smaller company behind — not as polished as Mailchimp.
License: GPL-3.0 Self-host difficulty: 4/5 Hosted cloud option

Mautic homepage · Source on GitHub · Mailgun vs Mautic →

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