smtp4dev

smtp4dev offers a controlled environment for simulating email workflows by acting as a dummy SMTP server on Windows, Linux, and Mac OS-X. It captures outgoing emails, provides IMAP/POP3 access for management, and logs SMTP interactions. Features include UTF8 support, viewport switching for device testing, multipart MIME inspection, and HTML validation. The server supports TLS/SSL with auto-cert generation, authentication, and multiple mailboxes with rules to direct messages. Users can relay, compose, or auto-reply to emails and employ scripting to simulate errors, ensuring thorough testing without impacting real-world email systems.