smtp4dev is a fake SMTP email server for development and testing that runs on Windows, Linux, and macOS.
The tool solves the problem of testing email functionality without risking real customer communication. It intercepts SMTP traffic from your application and stores messages for inspection. Beyond basic SMTP interception, smtp4dev offers a Terminal User Interface mode with full functionality, an advanced web interface, IMAP and POP3 access to retrieve messages, detailed SMTP session logging, HTML email rendering with compatibility reports, a viewport switcher for responsive email testing, MIME parts inspection, TLS/SSL support with automatic self-signed certificate generation, authentication, multiple mailboxes with routing rules, message relay with rules, message composition and reply capabilities, and scripting expressions for error simulation.
Developers should choose this tool if they need comprehensive email testing beyond simple SMTP capture. It suits projects where email rendering quality matters, where you need to test multiple mailbox scenarios, or where you want to simulate authentication and TLS configurations. The README directly compares smtp4dev to MailHog, MailCatcher, MailDev, and FakeSMTP, highlighting that smtp4dev uniquely offers a full-featured Terminal UI, HTML compatibility reports, a MIME parts inspector, detailed SMTP session logging, multiple mailboxes with rules, and message composition features. The tool runs on .NET and supports Docker deployment.
The maintainers typically respond to new issues and pull requests within a day. Work in the issue tracker is dominated by requests for more details, suggesting that issue reports often lack sufficient information for immediate action.
