smtp4dev

Spec sheet

Purpose

smtp4dev is a fake SMTP server for development and testing, letting developers test email without sending it to real customers.Read 8 Oct 2026 · github.com

Platforms

The project offers Windows and Linux binaries and containers, plus a .NET SDK tool for platforms where the SDK is available; its README also names Mac OS X.Read 8 Oct 2026 · github.com

Deployment

Installation options include winget, Docker/OCI images, a .NET global tool, and GitHub release downloads.Read 8 Oct 2026 · github.com

API

The project provides an OpenAPI/Swagger API.Read 8 Oct 2026 · github.com

License

The GitHub repository identifies the project license as BSD-3-Clause.Read 8 Oct 2026 · github.com

API and automation

An API is available for automated tests and external applications, with endpoints for messages, sessions, mailboxes, and server status and configuration.Read 8 Oct 2026 · github.com

Client integration

Applications can connect by SMTP using the host and port where smtp4dev runs; the documentation gives localhost and port 25 as defaults.Read 8 Oct 2026 · github.com

Configuration

Settings can be changed in the UI, appsettings.json, environment variables, or command-line arguments.Read 8 Oct 2026 · github.com

Docker security

The maintainer warns that Docker-published ports may be accessible outside the host and recommends binding to 127.0.0.1 when external access is not needed.Read 8 Oct 2026 · github.com

Email protocols

It supports SMTP and provides IMAP and POP3 access to retrieve and delete messages.Read 8 Oct 2026 · github.com

Mail handling

Users can configure multiple mailboxes and routing rules, compose or reply to messages, and relay messages with optional automatic rules.Read 8 Oct 2026 · github.com

Mail protocols

It supports SMTP, IMAP, and POP3 for receiving, retrieving, and deleting test messages.Read 8 Oct 2026 · github.com

Message inspection

Features include SMTP session logs, multipart MIME inspection, HTML rendering, validation, and compatibility reports.Read 8 Oct 2026 · github.com

Platforms and distribution

The project offers Windows and Linux binaries and containers, and a .NET SDK tool for platforms where the SDK is available; its README also names Windows, Linux, and Mac OS X.Read 8 Oct 2026 · github.com

Security configuration

The Docker security guide warns that published ports may expose captured emails externally and recommends binding ports to localhost unless outside access is needed.Read 8 Oct 2026 · github.com

Security features

It supports TLS/SSL with implicit and STARTTLS modes, automatically generated self-signed certificates, and optional authentication.Read 8 Oct 2026 · github.com

SMTP debugging

The product provides SMTP session logging and supports scripting expressions for error simulation.Read 8 Oct 2026 · github.com

Testing integrations

The testing guide covers programmatic use with the REST API, SignalR email notifications, Testcontainers examples for multiple programming languages, and direct use of the SMTP server component in .NET.Read 8 Oct 2026 · github.com

Testing tools

The interface includes a viewport size switcher for simulating mobile email views and a terminal UI with full functionality.Read 8 Oct 2026 · github.com

Who it is for

The README describes it for advanced email development and testing, production-like testing, development teams, and CI/CD pipelines.Read 8 Oct 2026 · github.com

Windows requirement

The winget instructions specify Windows 10 version 1809 (build 17763) or newer.Read 8 Oct 2026 · github.com

Where Specifiction places it

• Email Testing Software#23 of 287.2