Connecting directly to Gmail requires OAuth 2.0 authentication — this can't be done entirely in a browser app without a backend server due to Google's security policies. Here's how to get it working:
1Go to Google Cloud Console → Create a project → Enable Gmail API
2Create OAuth 2.0 credentials (Web Application type) and set http://localhost as authorized origin
3Copy your Client ID below and click Connect — this app will read your spam folder senders
4All lookups happen locally in your browser. Nothing is sent to any external server except public WHOIS APIs.