SMTPProof

SMTPProof is a web app (with a lightweight desktop agent) that continuously tests your SMTP server’s real-world deliverability and authentication posture. It sends scheduled, low-volume test messages to a controlled seed list across major mailbox providers, then correlates outcomes with SMTP logs to pinpoint whether failures come from DNS (SPF/DKIM/DMARC), TLS/cipher issues, reverse DNS, rate limits, content filtering, or IP/domain reputation shifts. The product focuses on actionable diagnostics: exact failing handshake step, recommended config changes, and a “blast radius” estimate (which domains are affected). It also tracks changes over time, alerting when a deploy, certificate renewal, or DNS edit causes a sudden drop in inbox placement. This is not an email marketing tool; it’s an ops-grade monitoring and troubleshooting layer for teams running their own SMTP infrastructure or using relays.