Read receipts that actually mean read.
Every other email tool fires “opened!” the moment Apple Mail prefetches the pixel. Signum runs six independent signals on every email, filters out MPP and scanner bots, and scores real engagement in real time. Score-aware follow-ups draft themselves.
No credit card · 2-minute setup · Chrome extension or Gmail addon
One signal can lie.
Six can't.
Each signal lives in a different part of the email HTML. Each fires from a different system in the recipient's client. When they corroborate, we know. When they don't, we say so.
Pixel GIF
<img src=".../px/{token}.gif">A 1×1 transparent image. The classic tracking signal.
Most blocked, often faked. We use it as one of six, never alone.
CSS Beacon
<link rel="stylesheet" href=".../c/{token}.css">A stylesheet load. Separate cache rules, separate network call.
Fires even when image loading is disabled by the client.
Font Beacon
@font-face { src: url(".../f/{token}.woff") }A @font-face declaration. Loads on layout, not image fetch.
Survives clients that block images aggressively. Triple-confirms read.
DNS Wildcard
<img src="//{token}.px.signum.email/1.gif">A unique subdomain. The DNS lookup itself is the signal.
Image proxies cannot cache it. Last-resort confirmation.
Link Click
<a href=".../go/{token}?u=...">Active engagement. The recipient deliberately clicked.
Bot click bursts (3+ links in 2s) get filtered as URL detonation.
Gmail API
GET /gmail/v1/users/me/messages/{id}Ground truth. The Gmail API directly reports the read.
Requires the Workspace Addon. When it fires, you know.
score = pixel + css + font + dns + min(click, 60) + api − deductionsclamped 0–100 · tiers: NO_SIGNAL 0–30 · LIKELY 31–60 · ENGAGED 61–85 · CONFIRMED 86–100Signum isn't just a tracker.
It's how you run email.
Detection is the floor, not the ceiling. Signum scores engagement, automates follow-ups, tracks documents, drafts replies with AI, and respects every recipient's privacy — in one product.
See what really happened.
Six independent signals
Pixel, CSS, font, DNS, link click, and Gmail API — all firing in parallel from different parts of the email.
Six-layer bot filtering
UA blocklist, IP classifier, timing window, click-burst detection, honeypot — every event filtered before it counts.
Engagement scoring
Every read gets a 0–100 score and one of four tiers — Confirmed, Engaged, Likely, No-signal.
Do something with what you see.
Score-aware follow-ups
Send a different follow-up to someone who scored 87 vs someone who scored 25. Branching rules built in.
AI follow-up drafts
Claude generates a follow-up in your voice based on the recipient's engagement depth and your past replies.
Document tracking
Track which pages of an attached PDF were read and for how long. Per-page heatmaps included.
Watch engagement happen live.
Real-time notifications
A toast slides in the moment someone reads. Recipient name, score, location, device — all in one glance.
Per-recipient timeline
See every signal fire chronologically for each recipient. Every open, every click, every scroll.
Reply & forward detection
Know when a recipient forwarded your email and the second-degree reader engaged with it.
Privacy is the product.
Per-workspace encryption
Subject lines, recipient emails, and IPs are encrypted with a key that's unique to your workspace.
One-click opt-out
Every email footer carries a visible opt-out link. Recipients control their inclusion in tracking.
Teams & roles
Share rules and templates across your team. Admin console, granular permissions, shared analytics.
Most trackers count opens.
Signum tells you what happened.
Open tracking became a commodity years ago. Bot filtering is catching up. What's still missing — and what Signum is built around — is the engagement intelligence above all that: scoring, document analytics, score-aware workflows, and AI.
Public pricing as of 2026 · capabilities verified from vendor documentation
Your data, locked.
Their data, respected.
We hold sender data behind workspace-level encryption and honour recipient opt-outs as policy. Privacy isn't a checkbox — it's how the product is built.
Encrypted from end to end.
Every subject line, recipient email, and event is encrypted with a key unique to your workspace. Even if our database leaked, your data is unreadable.
Your recipients stay in control.
Every email carries a visible "opt out" link. Recipients can opt out in one click — no account, no friction. Their choice is honored everywhere Signum operates.
Built to clear procurement.
GDPR-ready, audit-ready, with a signed Data Processing Agreement on request. Full data export and delete are self-serve. No surprises for your security team.
We never sell tracking data. We never share it outside your workspace. You can export everything you've ever stored, and delete it forever, from your settings.
Three places.
One Signum.
A browser extension that adds Signum to Gmail compose. An official Google add-on for ground-truth reads. A web dashboard that ties it all together — on any device.
Browser extension
Right inside Gmail.
- Adds a Signum switch next to Send
- No setup beyond installing it
- Real-time notifications as people read
- Works everywhere Chrome works
Gmail add-on
Official Google integration.
- Lives in the Gmail sidebar on every device
- Uses Google's sanctioned APIs
- Confirmed-read signal with high accuracy
- IT-friendly: deploys to a whole team in minutes
Web dashboard
Where your engagement story lives.
- Live feed of every read, click, and reply
- Per-recipient timelines and scores
- Build follow-up rules and AI drafts
- Read on phone, tablet, or desktop
People who can't afford fake data.
Founders pitching investors. SDRs working a quota. IR teams tracking 200 LPs. When the cost of a wrong follow-up is high, accurate engagement data isn't a nice-to-have.
Know which investors actually read the deck.
You sent the deck to 40 VCs. 38 inboxes "opened" it within 3 minutes. Three were humans. Signum tells you which three.
Stop chasing fake opens before coffee.
Your SDRs wake up to 200 "opens" overnight. Most are MPP. Signum filters them, ranks the rest by score, and surfaces the 12 worth a follow-up call today.
Know which LPs read the letter.
You sent the quarterly update to 200 LPs. With Signum, see exactly who read it, who reached page 4 of the PDF, and who hasn't opened it yet — by Tuesday morning.
Less than a coffee.
More accurate than your CRM.
Free for your first 100 emails. Paid plans start at $4.99 — the kind of price you upgrade to without thinking. No seat tax, no surprise fees, cancel any time.
Free
For curious users- 100 tracked emails per month
- All six detection signals
- Six-layer bot filtering
- Real-time dashboard
- Chrome Extension
- Single user
Standard
For everyday senders- Unlimited tracked emails
- Workspace Addon (Gmail API)
- Real-time notifications
- Follow-up rules
- Document tracking
- Priority email support
Premium
For teams and power users- Everything in Standard
- AI follow-up drafts (Claude)
- AI persona that learns your style
- Team workspace (up to 5 seats)
- Slack / Teams integration
- Concierge onboarding
Need more than 5 seats? · Talk to us about Teams
The questions everyone asks.
No. We ship two distribution channels. The Chrome Extension adds a Signum toggle inside Gmail compose — it reads the DOM, it doesn't scrape anything. The Workspace Addon uses Google's sanctioned APIs and goes through Google's Marketplace review. Use either or both.
They count every pixel fire as an open. We count six independent signals, run every event through a six-layer bot filter, and score the result 0–100. Same data — different conclusion. Where they report "opened," we report what actually happened.
Every tracked email carries a visible opt-out link in the footer. Recipients can opt out per-sender or globally with one click — no account required. We never sell tracking data and never share it outside your workspace. Our privacy policy is written in plain language. GDPR-aligned and built to clear procurement reviews globally.
Not yet. We focus on emails composed directly in Gmail today. For bulk cold email tooling, you should use the platform's built-in tracking. BCC-tracking and SMTP relay support are on the roadmap for V2.
Bounded by what the recipient's client allows. When the Gmail API (via the Workspace Addon) confirms a read, we hit 90+ with near-certainty. When only the pixel fires, we score 20 and mark it LIKELY. We never claim certainty we don't have — that's the entire pitch.
Postgres on Neon (US-East). Document attachments on Cloudflare R2. Pixel ingest on Cloudflare's global edge for <50ms latency. Sensitive fields (recipient email, subject, IP) are encrypted at the application layer using per-workspace keys derived from a master pepper in GCP Secret Manager — one tenant's compromise can't cascade to another.
Yes. Settings → Data → Export downloads everything as a JSON archive. Delete is self-serve with a 24-hour grace period in case of mis-clicks. We hard-delete after the grace period — no soft-delete shadow copies.
Pro and Top scale to 25 seats. Above that, we have an Enterprise tier with SSO, admin console, shared workspace, and a Data Processing Agreement. Email us — we'll set up a 30-min call.
Axiom Tech Lab — a small, focused team building globally. Built by people who've sent enough cold email to know how broken the existing tools are. Signum is our flagship product.
Stop guessing.
Start knowing.
Free for your first 200 emails per month. No credit card. No "verified by" footer. Real engagement data, finally.
Built for global teams · Founders, sales pros, IR · v1.0