Email Testing Tools Comparison: Mailpit vs MailHog vs Mailtrap vs smtp4dev

Several tools exist for intercepting and testing emails during development. They all solve the same core problem — capturing outgoing SMTP traffic without delivering it — but differ in features, maintenance status, and hosting model.

The Candidates

Mailpit

The current best choice for self-hosted email testing. Mailpit is actively maintained, has excellent Docker support, and exposes a clean REST API.

Setup:

docker run -d -p 1025:1025 -p 8025:8025 axllent/mailpit

API quality: Excellent. HTML and Text are top-level fields — no MIME parsing required.

{
  "ID": "abc123",
  "From": { "Address": "from@example.com" },
  "To": [{ "Address": "to@example.com" }],
  "Subject": "Hello",
  "HTML": "<p>Hello</p>",
  "Text": "Hello"
}

Key features:

• Full-text search over messages
• Message tagging
• SMTP authentication support
• Per-recipient filtering
• Prometheus metrics endpoint
• Optional persistence (SQLite)

Best for: New projects, teams that want a self-hosted solution with an active community.

MailHog

The original Go-based email testing tool. Still widely used due to years of documentation and tutorials, but has not had a release since 2017.

Setup:

docker run -d -p 1025:1025 -p 8025:8025 mailhog/mailhog

API quality: Works but requires MIME parsing to extract HTML.

// MailHog requires navigating MIME parts
const htmlPart = message.MIME.Parts
  .find(p => p.Headers['Content-Type'][0].includes('text/html'))
const html = htmlPart?.Body || ''

Key features:

• Stable and battle-tested
• Huge ecosystem of examples and tutorials
• v2 API for listing messages

Best for: Existing projects already using MailHog. No reason to migrate, but use Mailpit for new projects.

Mailtrap

A cloud SaaS solution that requires no local setup. Mailtrap provides a managed SMTP sandbox plus a web UI for team collaboration.

Setup:

# .env.test — use Mailtrap's SMTP endpoint
SMTP_HOST=sandbox.smtp.mailtrap.io
SMTP_PORT=2525
SMTP_USER=your-mailtrap-user
SMTP_PASS=your-mailtrap-pass

API quality: Good REST API, requires account/inbox IDs and API token.

Key features:

• Shared team inbox — multiple devs see the same emails
• Spam score analysis
• HTML email preview across clients (paid)
• Email Analytics (paid)
• Mailtrap Email Sending (production SMTP, separate product)

Limitations:

• Requires internet access — no offline or air-gapped CI
• API requires account setup and credentials in CI secrets
• Rate limits on free tier
• Privacy consideration: emails sent to a third-party cloud

Best for: Teams that want shared visibility without local setup, or that already use Mailtrap's production sending product.

smtp4dev

A .NET-based self-hosted SMTP server with a web UI. Less common in the Node.js/Python ecosystem but popular in .NET shops.

Setup:

docker run -d -p 25:25 -p 80:80 rnwood/smtp4dev

API: REST API available at http://localhost:80/api/

Best for: .NET/ASP.NET projects where the team is already in the .NET ecosystem.

Feature Comparison

CI Integration

All self-hosted tools work as GitHub Actions services:

# Mailpit (recommended)
services:
  mailpit:
    image: axllent/mailpit
    ports:
      - 1025:1025
      - 8025:8025

# MailHog (legacy projects)
services:
  mailhog:
    image: mailhog/mailhog
    ports:
      - 1025:1025
      - 8025:8025

Mailtrap uses environment variables (API credentials) rather than a Docker service.

Decision Guide

New project, self-hosted preferred → Mailpit Clean API, active maintenance, easy Docker setup. No reason not to use it.

Existing project already using MailHog → Keep MailHog MailHog works fine. Migration effort not worth it unless you need search or persistence.

Team needs shared visibility without local tooling → Mailtrap The only option where multiple developers share the same email inbox without running local servers.

ASP.NET / .NET project → smtp4dev Native .NET tooling, integrates well with the Visual Studio ecosystem.

Migration from MailHog to Mailpit

The Docker image and port change is the only difference:

- image: mailhog/mailhog
+ image: axllent/mailpit

The main code change: stop parsing MIME parts. Mailpit returns HTML and Text directly at the message level.

- const html = msg.MIME.Parts.find(p => p.Headers['Content-Type'][0].includes('text/html'))?.Body
+ const html = msg.HTML

That's it. API endpoints differ (/api/v2/messages → /api/v1/messages) but the structure is close enough that most helpers need minimal changes.