InboxStack is an email deliverability intelligence platform built around Brain, a proprietary causal AI engine that identifies why emails miss the inbox — not just that they did. Most deliverability tools stop at monitoring: they show a drop in inbox placement or a blocklist hit and leave you to investigate. InboxStack goes further, correlating signals from your ESP, DNS authentication records (SPF, DKIM, DMARC), Google Postmaster Tools, Microsoft SNDS, and 50+ blocklists through a causal knowledge graph built on a 22-year deliverability knowledge base — tracing the actual root cause, whether it's a DKIM misalignment, IP reputation dip, or content trigger.

Onboarding starts with forwarding your email headers for an instant DNS/auth audit, no migration required. Teams that want ongoing monitoring can connect their ESP and Postmaster accounts, with optional seed testing for real inbox-vs-spam placement data.

Built especially for digital agencies managing multiple client domains, and any team sending email at scale that's tired of dashboards that flag problems without explaining them.