InboxStack is an email deliverability intelligence platform built for teams who need to know why their emails aren't reaching the inbox — not just that they aren't. At its core is Brain, a proprietary causal AI engine trained on a 22-year deliverability knowledge base, which correlates signals across your ESP, DNS authentication records (SPF, DKIM, DMARC), Google Postmaster Tools, Microsoft SNDS, and 50+ blocklists to pinpoint root causes instead of surfacing raw metrics.

Most deliverability tools stop at monitoring: they show you a drop in inbox placement or a blocklist hit and leave you to investigate. InboxStack goes further, tracing the actual causal chain — a DKIM misalignment, a reputation dip on a specific sending IP, a content trigger — so you can fix the real problem instead of guessing.

Setup takes minutes with no migration required: forward your email headers for an instant DNS/authentication audit, or connect your existing ESP and Postmaster accounts for ongoing monitoring. Optional seed testing gives you real inbox-vs-spam placement data across major providers.

Built for agencies managing multiple client domains and growing companies who've outgrown basic authentication checkers, InboxStack turns deliverability from a black box into a diagnosable, fixable system.

Free Uptime Monitoring

Minimize your downtime by being the first to know about it! Start off with 15 Uptime Monitors, checked every 1 minute, from around the world, completely FREE forever.

Uptime Monitor features included for free:

• Accurate downtime detection, checking your website/server from around the world simultaneously
• Public Uptime Status Page
• Server Resource Usage Monitoring
• Public/Private Uptime Reports
• SSL Validity/Hostname Monitor
• SSL Expiration Monitor
• Domain Name Expiration Monitor
• Nameservers Change Detection
• Maintenance Mode + Schedule Maintenance + One-click Maintenance
• much more

Free Blacklist Monitor

The simple, yet effective way of monitoring all of your IPs & Domains and notice if any of them get blacklisted on the most popular blacklists, so you can immediately take action to find the cause and start the delisting procedures, before it gets to affect your clients or your network reputation.

Why HetrixTools?

• The user interface is extremely fast and simple to work with, no need to load countless pages to get things done
• We're constantly developing and improving the platform to get even better and contain more features
• If you're willing to spend 5 minutes of your time to try out our platform you'll see everything mentioned above for yourself