Papercut SMTP

The simple email receiver and viewer for development. Papercut SMTP is a 2-in-1 quick email viewer and built-in SMTP server. It catches every email your application sends — and delivers none of them.

The Problem

If you send emails from an application during development, you know the fear of a test email escaping into the wild. Are you positive none of those "test" emails are addressed to colleagues — or worse, customers? Setting up and maintaining a real test email server is a chore, and waiting for test emails to arrive slows your development cycle.

The Solution

Point your application at Papercut SMTP instead of a real mail server. It accepts every message instantly, stores it locally, and shows it to you — body, HTML, headers, attachments, right down to the raw encoded bits. Nothing is ever delivered.

Features

• Instant notifications when a new email arrives — Papercut sits quietly in the tray until it has something to show you
• Full email inspection — rendered HTML, plain text body, headers, MIME parts, attachments, and raw source
• Zero configuration — start the app and it's already listening on 127.0.0.1:25
• Optional background service with a browser-based web UI, for receiving email even when the desktop app isn't running
• Docker image for containerized development environments and CI
• Rules — automatically forward or relay received messages when needed
• TLS/STARTTLS and SMTP AUTH support for testing secure email flows

Quick Start

1. Install Papercut SMTP and run it — it immediately listens on 127.0.0.1:25.
2. Point your application at host localhost, port 25, no credentials.
3. Send an email from your app — it pops up in Papercut. That's it.

New to Papercut?

Read How It Works — a two-minute explanation of what Papercut is (and isn't).

License

Papercut SMTP is licensed under the Apache License, Version 2.0.