Mailinator
Disposable email testing inboxes with public and private domains
Papercut
Desktop SMTP server and email viewer for development
Papercut SMTP combines a local SMTP server with an instant email viewer, letting developers safely test application emails without risk of sending to real recipients.
Overview
Safe Email Testing for Developers
Papercut SMTP solves a critical development problem: testing application emails without the risk of accidentally sending messages to real users. This 2-in-1 tool combines a receive-only SMTP server with a rich desktop email viewer, eliminating the need to configure and maintain separate test mail infrastructure.
Instant Feedback, Zero Risk
Designed for developers building applications or websites that send email, Papercut SMTP captures all outbound messages locally and displays them immediately. View complete email details including HTML rendering, headers, MIME sections, attachments, and raw encoded content. The desktop app runs quietly in the system tray and provides notifications when new messages arrive, accelerating your development cycle.
Flexible Deployment Options
Available as a Windows desktop application (32-bit and 64-bit installers), an optional background service for always-on email capture, or a Docker container for containerized workflows. The service component includes an HTTP interface accessible at port 8080, enabling team-wide email testing environments. Built with C# and WPF, Papercut SMTP requires Microsoft WebView2 for the desktop UI.
Highlights
Built-in SMTP server (receive-only) with instant desktop email viewer
Complete email inspection: HTML rendering, headers, MIME sections, attachments, and raw view
System tray integration with new message notifications
Multiple deployment options: desktop app, Windows service, or Docker container
Pros
- Zero-configuration SMTP server eliminates test email infrastructure overhead
- Instant email viewing accelerates development and debugging cycles
- No risk of test emails reaching real recipients or customers
- Flexible deployment with desktop, service, and Docker options
Considerations
- Windows-only desktop application (requires WebView2 component)
- Receive-only server cannot test actual email delivery or routing
- Limited to local or containerized environments, not cloud-native
- No built-in collaboration features for team-based testing
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Fit guide
Great for
- Solo developers and small teams testing email functionality locally
- Windows-based development environments needing quick email verification
- Projects requiring detailed inspection of email structure and encoding
- Teams wanting Docker-based shared email testing environments
Not ideal when
- Production email sending or relay requirements
- Testing actual email deliverability or spam filter behavior
- macOS or Linux desktop users without Docker
- Large distributed teams needing cloud-based email testing platforms
How teams use it
Web Application Registration Flow Testing
Developers verify welcome emails, activation links, and HTML rendering without configuring external SMTP servers or risking accidental sends to real addresses.
E-commerce Order Confirmation Debugging
QA teams inspect order confirmation emails, validate dynamic content insertion, and review attachment formatting before production deployment.
Continuous Integration Email Validation
Automated test suites send emails to Dockerized Papercut SMTP instances, enabling programmatic verification of email content and structure in CI/CD pipelines.
Email Template Development and Preview
Designers and developers iterate rapidly on HTML email templates, viewing real-time rendering and MIME structure without waiting for external mail services.
Tech snapshot
C#91%
CSS3%
JavaScript2%
HTML2%
PowerShell1%
Batchfile1%
Frequently asked questions
Does Papercut SMTP actually send emails to recipients?
No. Papercut SMTP is a receive-only server designed exclusively for development. It captures emails locally and displays them in the viewer without forwarding to real addresses.
What platforms does the desktop application support?
The desktop application runs on Windows (32-bit and 64-bit). It requires Microsoft WebView2. Docker deployment is cross-platform.
Can I use Papercut SMTP with my existing application code?
Yes. Point your application's SMTP configuration to localhost:25 (or your chosen port). Papercut SMTP accepts standard SMTP connections without authentication requirements.
What is the difference between the desktop app and the service?
The desktop app includes the UI and SMTP server. The optional service runs the SMTP server and HTTP interface in the background, capturing emails even when the desktop client isn't running.
Project at a glance
Active- Stars
- 3,258
- Watchers
- 3,258
- Forks
- 296
Repo age10 years old
Last commit4 weeks ago
Primary languageC#
Last synced 4 hours ago