The SMTP Testing Tool
A free, lightweight Windows utility that opens a real SMTP conversation with any mail server — so you can prove out hosts, ports, TLS, authentication, and delivery in seconds, and see exactly what the server says back.
Windows 10 / 11 & Windows Server · ~560 KB · No installation required
Download & run
Grab SMTPTester.exe and double-click it. Nothing to install — the GUI opens straight away.
Enter your server details
Type the host, port, and TLS mode, add credentials if your provider needs them, then set the from/to addresses for a test message.
Send and read the log
Click send and watch the live SMTP transcript. Green means delivered; any error code and message is right there to act on.