
InboxStack
GlockApps
Email Testing By Inbox Pirates
MxToolBox
Folderly
HetrixTools
Inbox AI
InboxPro
Validity LLC
Sirius
Return Path
Inbox Mailers
J-2LLC
emailexpert
Sender Reputation
ZaapIT
InboxStack is an email deliverability intelligence platform built for teams who need to know why their emails aren't reaching the inbox โ 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 โ a DKIM misalignment, a reputation dip on a specific sending IP, a content trigger โ 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.
InboxStack
Validity LLCGlockApps - G-Lock Apps is an interesting tool that might seem simple to some, but is quite essential to most online marketers.
Sirius - An open-source clone of Siri from UMICH
Email Testing By Inbox Pirates - Preview, Analyze & Test emails with one click.
Return Path - Inbox placement solutions from Return Path helps improve email deliverability and increases email marketing ROI.
MxToolBox - All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool.
Inbox Mailers - Inbox Mailers enable brands the ability to know when subscribers are in their inbox while triggering an email that's generating a 3x โ 5x higher open rate, and a 1x โ 2x higher click-through rate! We call it VTO or View Time Optimization