Simplify Email Testing with a Local Papercut SMTP Server Using Docker

Testing email functionality in applications often involves configuring SMTP servers, dealing with spam filters, or worrying about unintentionally sending emails to real users. Enter Papercut SMTP, a lightweight and effective solution for email testing that simplifies the process.

This article explores how to set up and use Papercut SMTP with Docker, highlighting its use case, advantages, and how it fits seamlessly into a developer’s workflow.

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Why Use Papercut SMTP?

Papercut SMTP is designed to capture and display emails sent by applications for testing purposes. Instead of routing emails to actual recipients, it provides a safe, local environment to inspect email content, debug issues, and ensure the intended functionality.

Key Use Cases:

1. Application Development: Test email notifications, password resets, or transactional emails.
2. Safe Email Debugging: Avoid unintentional email delivery to real users during development or staging.
3. Integration Testing: Verify email generation and content within automated CI/CD pipelines.

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Benefits of Using Papercut SMTP

1. User-Friendly Web Interface: Papercut SMTP includes a simple web interface for viewing and managing captured emails, eliminating the need for additional email clients.
2. Quick Setup: The lightweight design and Docker compatibility ensure that you can spin up the server in minutes without complex configurations.
3. Efficient Resource Usage: Unlike traditional SMTP servers, Papercut runs locally with minimal overhead, making it ideal for development and testing.
4. Controlled Environment: Local deployment ensures that emails remain private and do not interfere with production systems.
5. Cross-Platform Support: Works seamlessly with any application that supports SMTP, regardless of the programming language or framework.

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How It Works

Papercut SMTP acts as a local SMTP server. When your application sends an email, Papercut intercepts it and displays the details in its web interface. The process is simple:

1. Your application connects to the SMTP server using the standard SMTP protocol.
2. Emails sent to the server are displayed in the Papercut SMTP web interface.
3. Developers can view, debug, and delete emails as needed, ensuring the application functions correctly.

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How To Setup

Here is the docker compose file for the papercut SMTP server.

services:
  papercut:
    image: changemakerstudiosus/papercut-smtp:latest
    container_name: papercut_smtp
    ports:
      - "8080:80"
      - "25:25"

• Map port 8080 or your preferred port on the host to port 80 in the container for the web interface
• Map port 25 on the host to port 25 in the container for SMTP

Run docker compose up -d to start the service.

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How to setup SMTP Configuration

In your application, configure the email settings to point to the local Papercut SMTP server. Use the following details:

• SMTP Host: localhost or the server's IP address (if on a remote machine).
• SMTP Port: 25.
• No Authentication: Papercut SMTP does not require authentication for local use.
• No SSL: Papercut SMTP does not require SSL for local use.

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Optimizing Workflow with Papercut SMTP

Simplified Development

Instead of managing complex SMTP configurations or relying on third-party services during development, Papercut SMTP offers a local, no-risk solution. It streamlines the development process by providing immediate feedback on emails without the risk of delivering them to actual users.

Integration with CI/CD

Integrate Papercut SMTP into your testing pipeline to automatically validate email generation during builds. Whether it’s confirming the presence of specific text in an email or ensuring attachments are correctly added, Papercut SMTP can handle it.

Troubleshooting and Debugging

The web interface allows you to inspect:

• Email headers for debugging routing issues.
• HTML and text content for design and formatting validation.
• Attachments to ensure they’re correctly included.

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Tips for Efficient Usage

1. Automate Cleanup: If you’re running tests frequently, schedule regular email cleanup in the interface to avoid clutter.
2. Secure Your Setup: Even though Papercut is for local use, consider firewall rules or access restrictions to limit exposure.
3. Integrate Tools: Combine Papercut with email design tools like MJML to streamline the development and preview process.

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Wrapping Up

Papercut SMTP is an invaluable tool for developers and teams working with email functionality. It ensures a controlled, efficient, and hassle-free environment for testing emails, making it a must-have for modern development workflows. Whether you’re debugging a password reset feature or verifying transactional email templates, Papercut SMTP offers simplicity and reliability.

Set it up in your development environment today, and take the stress out of email testing!