smtp-tool

SMTP Tool is a lightweight, high-performance Windows desktop application designed for developers, DevOps engineers, and system administrators to test, diagnose, benchmark, and debug SMTP mail servers. Built on .NET Framework 4.8, it offers a comprehensive suite of features including support for TLS 1.2/1.3, STARTTLS, and various authentication methods (AUTH LOGIN, AUTH PLAIN). Key capabilities include a built-in local HTTP tracking server for simulating real-time email opens and clicks, step-by-step latency benchmarking (DNS, TCP, TLS, DATA), and an interactive Telnet SMTP terminal for protocol-level debugging. The tool supports pre-configured profiles for major providers like Gmail, Microsoft 365, and Amazon SES, and includes clean EML templates for transactional emails. It is a portable, zero-dependency executable that works on Windows 7 through Windows 11 and Server editions.