SMTP Debug is a free and secure tool that can be used to diagnose SMTP connectivity issues.
This tool connects your SMTP server and initiates a testing session. It then provides a detailed log detailing the interaction between servers. This tool simplifies troubleshooting, and helps resolve sending issues, whether you're using popular services like SendGrid or Google SMTP.
Your information is private and secure with end-to-end encrypted communication.
The tool does not store session logs or credentials. You can enhance security further by changing your password or using the optional SMTP Blackhole feature.