Best Open Source Email Marketing Tools in 2026

TL;DR

Mailchimp charges $299/month for 50,000 subscribers. Self-hosting Listmonk on a $10/month VPS with Amazon SES for email delivery costs $10–15/month total — a 95% cost reduction. Listmonk is the best single-binary newsletter engine for high-volume sending. Mautic is the open source HubSpot Marketing Hub replacement. Postal replaces Mailgun and SendGrid for transactional email infrastructure.

Key Takeaways

Listmonk (AGPL-3.0, 15K+ stars) is a single Go binary that sends 100K+ emails/hour from 50 MB RAM — the most efficient email tool in any language
Mautic (GPL-3.0, 7K+ stars) provides full marketing automation: lead scoring, multi-channel campaigns, A/B testing, and CRM integration
Postal (MIT) is a complete mail server platform replacing Mailgun/SendGrid for transactional and marketing email delivery
Keila (AGPL-3.0) is the modern Elixir-based newsletter tool with real-time analytics and the cleanest editor
Mailtrain (GPL-3.0) handles newsletter campaigns with RSS-to-email and multiple SMTP provider support
At 50K subscribers, Mailchimp costs $3,588/year vs $120–180/year for Listmonk + SES

The Email Marketing Cost Trap

Email marketing is one of the most cost-elastic categories in software. Pricing is subscriber-based, which means costs scale directly with business success. Mailchimp charges more the more your business grows — the opposite of a healthy pricing relationship.

At 10K subscribers, Mailchimp Standard is $100/month ($1,200/year). At 50K subscribers, it's $299/month ($3,588/year). At 200K subscribers, you're in a custom pricing conversation. ConvertKit's pricing structure is similar: $66/month at 10K, $119/month at 25K.

The actual cost of sending email is nearly free at these volumes. Amazon SES charges $0.10 per 1,000 emails — 50K emails/month costs $5 on SES. The premium you pay Mailchimp isn't for the email delivery; it's for the dashboard, templates, and automation builder.

Self-hosted tools provide all of those features. You pay for the VPS ($5–15/month) and the SMTP service ($5–20/month for SES or Postmark). The difference stays in your pocket.

Listmonk — Best Performance and Efficiency

Listmonk is remarkable for what it achieves in a tiny footprint. The entire application is a single Go binary — no Node.js runtime, no Python environment, no JVM. It starts in milliseconds, runs on 50 MB RAM, and sends email at rates that exceed what Mailchimp's API would permit even on paid plans.

Campaign management in Listmonk covers subscriber lists with custom attributes, subscriber segments with boolean query logic, campaign scheduling, and delivery throttling. You can send a campaign to "subscribers who clicked the last 3 campaigns AND have the attribute plan=pro" using the segment query builder.

Template system uses Go's standard template syntax. This is more powerful than Mailchimp's drag-and-drop editor for developers, but requires HTML/CSS knowledge. The result is fully custom email templates that look exactly like your design, not a Mailchimp template with your logo swapped in.

# Listmonk Docker Compose
services:
  listmonk:
    image: listmonk/listmonk:latest
    restart: unless-stopped
    ports:
      - "9000:9000"
    environment:
      - LISTMONK_app__address=0.0.0.0:9000
      - LISTMONK_db__host=postgres
      - LISTMONK_db__port=5432
      - LISTMONK_db__user=listmonk
      - LISTMONK_db__password=listmonk
      - LISTMONK_db__database=listmonk
    volumes:
      - ./config.toml:/listmonk/config.toml
  postgres:
    image: postgres:15
    environment:
      POSTGRES_DB: listmonk
      POSTGRES_USER: listmonk
      POSTGRES_PASSWORD: listmonk
    volumes:
      - listmonk_db:/var/lib/postgresql/data
volumes:
  listmonk_db:

SMTP configuration is separate from Listmonk itself — you bring your own email delivery. Amazon SES is the most cost-effective at scale ($0.10/1K emails). Postmark ($1.50/1K) and Mailgun ($0.80/1K) offer higher deliverability for transactional content. You can configure multiple SMTP pools and Listmonk will load-balance across them for very high volume sends.

Transactional email API lets your application trigger individual emails (password resets, order confirmations, system alerts) through Listmonk using the same infrastructure as your campaigns. This consolidates your email delivery to a single tool.

Key features:

Single Go binary (50 MB RAM, zero dependencies)
100K+ emails/hour throughput
Subscriber management with custom attributes
Segment-based audience targeting (boolean queries)
Campaign scheduling and throttling
Go template system for email design
Double opt-in with customizable flows
Bounce and complaint handling (via webhook)
Open and click tracking
REST API for subscriber management and campaign triggering
Transactional email API
Multiple SMTP pool support

Mautic — Best Marketing Automation

Mautic is the open source equivalent of HubSpot Marketing Hub or Marketo. Where Listmonk focuses purely on email campaigns, Mautic orchestrates multi-channel marketing automation: email sequences, landing pages, web push notifications, SMS, and social media posting — all triggered by contact behavior.

The visual campaign builder lets you define automation workflows: when a contact submits a form, wait 2 days, send email A; if they click a link, add them to segment "interested," send email B, notify the sales team in Slack; if no click after 7 days, send email C. This behavioral automation is what separates marketing automation from simple email campaigns.

Lead scoring tracks contact engagement across all channels and assigns point values to actions (opened email = 1 point, clicked link = 5 points, visited pricing page = 10 points). When a contact crosses a score threshold, Mautic triggers a sales notification or moves them to a high-priority segment. This is the core of the marketing-to-sales handoff in B2B companies.

# Mautic with Docker
docker run -d \
  --name mautic \
  -p 8080:80 \
  -e MAUTIC_DB_HOST=your-mysql-host \
  -e MAUTIC_DB_USER=mautic \
  -e MAUTIC_DB_PASSWORD=password \
  -e MAUTIC_DB_NAME=mautic \
  -v mautic_data:/var/www/html/media \
  mautic/mautic:latest

Mautic requires MySQL/MariaDB and approximately 1 GB RAM. A cron job must run at regular intervals to process queued emails and automation triggers — this is a common gotcha in self-hosted Mautic setups.

Key features:

Email campaigns with drag-and-drop builder
Visual campaign workflow automation
Landing page builder
Lead scoring
Contact segmentation
A/B testing (emails and landing pages)
Multi-channel (email, SMS via Twilio, web push)
CRM integrations (Salesforce, Hubspot)
Form builder
Dynamic content (personalized email blocks)
Social monitoring

Postal — Self-Hosted Email Delivery Infrastructure

Postal is a different category from Listmonk and Mautic. It's a mail transfer agent (MTA) — the underlying email delivery infrastructure. Where Listmonk uses SES or Postmark to actually send email, Postal is the SMTP server.

Self-hosting Postal gives you a dedicated IP address for your domain's email, complete delivery logs, bounce handling, spam filtering, and your own email infrastructure. This is the open source replacement for Mailgun ($0.80/1K emails), SendGrid ($0.85/1K), or Postmark ($1.50/1K).

The economics are compelling at scale: Postal costs only your VPS hosting. At 500K emails/month, you save $400–750/month versus commercial SMTP services. Getting off a shared IP pool also gives you control over your sending reputation — no longer affected by other customers on the same Mailgun or SendGrid IP range.

Deliverability requires careful setup: Proper SPF, DKIM, and DMARC records, a dedicated IP with no spam history, and a proper IP warmup process. Self-hosting email delivery is not for the faint of heart — it's the option for teams with email expertise or those willing to develop it.

Keila is a newer Elixir-based newsletter tool with a polished interface and real-time analytics. If Listmonk's template system feels too developer-heavy, Keila's visual email builder (integrated with its own block-based editor) is more accessible.

Keila supports multiple campaigns per newsletter issue, subscriber tagging, double opt-in, and basic analytics (opens, clicks, unsubscribes). It's a good fit for creators and small publications who want a self-hosted ConvertKit experience without Mautic's complexity.

Full Comparison

Feature	Listmonk	Mautic	Postal	Keila
License	AGPL-3.0	GPL-3.0	MIT	AGPL-3.0
Min RAM	50 MB	1 GB	2 GB	512 MB
Newsletter Campaigns	✅	✅	❌ (delivery only)	✅
Marketing Automation	❌	✅ Full	❌	❌
Visual Email Builder	❌	✅	❌	✅
Landing Pages	❌	✅	❌	❌
SMTP Server	External	External	✅ Built-in	External
Lead Scoring	❌	✅	❌	❌
A/B Testing	❌	✅	❌	❌
REST API	✅	✅	✅	✅
Stack	Go	PHP	Ruby	Elixir

Decision Framework

Choose Listmonk if: You send newsletters or announcement campaigns and want maximum efficiency with minimal resources. Developer-friendly, not marketer-friendly.

Choose Mautic if: You need full marketing automation — multi-step email sequences, lead scoring, behavioral triggers, landing pages. HubSpot Marketing Hub on your own server.

Choose Postal if: You're large enough that commercial SMTP costs are significant and you have the expertise to manage your own email delivery infrastructure.

Choose Keila if: You want a polished self-hosted newsletter tool with a visual builder that's more accessible than Listmonk's template system.

Cost Comparison (50K subscribers)

Platform	Monthly Cost	Annual Cost
Mailchimp Standard	$299/month	$3,588
ConvertKit Creator	$119/month	$1,428
Listmonk + SES ($0.10/1K)	$10 VPS + $5 SES	$180
Mautic + SES	$15 VPS + $5 SES	$240

At 200K subscribers, Mailchimp enters custom pricing territory — typically $800+/month. Listmonk + SES costs $25–40/month at the same volume.

See open source alternatives to Mailchimp on OSSAlt.

Best Open Source Email Marketing Tools 2026