This tool is the most secure because you don't need to give us your SMTP credentials. You should configure your email-sending software (CMS, CRM, custom website) by adjusting these settings:
Press the Start button, and you will have 15 minutes to do the test - just send a message using your software with our settings, and you will see the full log of the SMTP session.
Unregistered users are limited to 10 test sessions per hour, while registered users can have up to 30 sessions per hour.
Please remember to store your original credentials in a safe place before changing them!