Browser Extension + AI Mailbox Firewall

Stop inbox threats before you click, send, or let an AI read your mail.

ThreadScanner inspects every message directly on your device. Protect Gmail and Outlook Web with real-time phishing verdicts, time-of-click link blocking, and outbound data-loss checks, and shield Claude, Cursor, and Windsurf from email prompt injection.

View plans & start free Install in 2 minutes
100% on-device message inspection One license unlocks Extension + MCP Free tier included (25 scans/day)
Gmail & Outlook Web · On-Device Guard
Action Required: Verify billing profile billing@paypa1-account.com
Likely phishing · Do not trust links Verified locally
  • Deceptive character-substitution domain spoofing PayPal
  • Reply-To address routes responses to an unrelated external host
  • Tracking link unwraps across 3 hops to a newly registered login page
Time-of-Click Guard
Blocked paypa1-account.com
Outbound Compose Guard
SSN, API keys & risky links checked
MCP Guarded Mailbox · Claude / Cursor / Windsurf Prompt-injection instructions detected in inbound thread
Body withheld
Two Surfaces · One License

Protection where you read email and where your AI agents act on it.

Email security gateways filter bulk spam at the perimeter, yet lookalike domains, hijacked threads, and hidden prompt injections still land in the inbox. ThreadScanner inspects messages at the moment of use.

Browser Extension Chrome · Edge · Brave

Webmail Protection for Gmail & Outlook

Real-time inbound and outbound security built directly into Gmail and Outlook on the web, with zero mail routing or MX record changes.

  • Inline risk verdicts & 6-layer scorecard: Clear warnings inside every thread covering authentication, sender identity, links, content, attachments, and threat-feed checks.
  • Time-of-click link protection: Holds flagged or redirect links for up to 1.6 seconds to unwrap multi-hop chains and block dangerous destinations before yielding.
  • Outbound Compose Guard: Warns before you send exposed SSNs, live API keys, external reply-all leaks, lookalike recipient domains, or forwarded phishing URLs.
  • Attachment & QR inspection: Evaluates document structures, embedded QR codes, and SHA-256 file hashes locally without uploading files.
Extension setup guide
MCP Server Claude · Cursor · Windsurf · Grok

Guarded Mailbox & Firewall for AI Agents

Give AI assistants safe access to email without exposing them to untrusted attacker instructions hidden inside HTML, headers, or quoted replies.

  • Automatic payload containment: High-risk messages and prompt injections have their raw body withheld automatically before reaching the model context window.
  • Guarded Mailbox tools: Search, list, and read Gmail or Microsoft 365 threads locally with structured trust envelopes attached to every result.
  • On-demand security tools: Expose scan_message, scan_url, and scan_attachment to any local stdio or OAuth-authenticated MCP client.
  • One-command host configuration: Auto-discovers installed MCP clients via npx @threadscanner/mcp setup and writes local owner-only (0600) host configuration entries.
MCP setup command
Detection & Prevention

Six layers of verification on every thread.

Deterministic analysis runs in milliseconds on your machine, paired with live domain intelligence when you want deeper verification.

Cryptographic Header Verification

Evaluates Received routing hops, Reply-To alignment, and anchored receiver authentication stamps locally offline, and re-verifies DKIM keys, SPF records, and DMARC policies over live DNS when online lookups are enabled.

Brand & Executive Impersonation

Catches homoglyphs, character substitutions, lookalike domains, display-name spoofing, Reply-To mismatches, and first-contact executive or vendor lures.

Time-of-Click & Redirect Unwrapping

Follows shortened and tracking URLs across multiple hops, checks newly registered domains via RDAP and certificate logs, and holds flagged links for up to 1.6 seconds on click to warn before dangerous destinations open.

Outbound DLP & Compose Guard

Inspects outgoing replies before they leave your outbox for SSNs/ITINs, cloud credentials, unexpected external recipients, and risky forwarded URLs.

Attachment & QR Code Analysis

Detects risky Office macros, double extensions, password-protected archives, QR-code phishing lures, and known malicious file hashes locally in WebAssembly.

AI Prompt-Injection Containment

Identifies hidden CSS/HTML text, zero-width characters, and system-prompt override attempts aimed at hijacking AI email assistants and MCP workflows.

Security Architecture

Enterprise-grade privacy by design.

Security software should never become a new data-exfiltration risk. ThreadScanner is architected so your raw messages stay on your hardware.

Zero server-side email storage

Message bodies, headers, and attachments are inspected on your device (with bounded local snapshots of up to 100 recent scanned messages kept in browser storage for instant verdicts and rescanning, clearable anytime). ThreadScanner servers never receive, log, or store the contents of your inbox.

Least-privilege mailbox access

Inspect opened Gmail and Outlook Web messages immediately with zero sign-in and no mail-send or mail-delete permissions. Optional connected-mailbox sync and one-click security report forwarding request only the scopes required when enabled.

Bring-your-own-key AI second opinion

Core detection is fast, deterministic, and requires no LLM. If you opt into AI second-opinion summaries, redacted metadata goes straight from your device to Anthropic, OpenAI, Google Gemini, xAI (Grok), or local Ollama using your own keys — single-model or multi-model consensus.

Offline cryptographic licensing

Licenses are signed TSL1 Ed25519 tokens verified locally without per-scan phone-home calls. This website ships zero third-party analytics, ad trackers, or external font scripts.

Pricing

Simple, transparent plans.

Start free in seconds. Every paid plan includes one unified license key for both the Browser Extension and the MCP Server.

Free

Essential inbox & local MCP checks for personal use.

$0 / forever

No credit card or account required

  • Up to 25 scans per day
  • Chrome & Edge extension for Gmail & Outlook Web
  • Core phishing, header & lookalike detection
  • Time-of-click blocking on flagged links
  • Local MCP scan_message tool
Chrome Web Store — coming soon
Most Popular

Individual

Full webmail & AI mailbox defense for professionals.

$9 / month

1 seat · billed monthly · cancel anytime

  • Unlimited webmail & MCP scans
  • Browser Extension + Full MCP Guarded Mailbox
  • Live DNS, RDAP domain-age & threat-feed lookups
  • Deep multi-hop redirect unwrapping
  • Outbound Compose Guard (SSN, keys & risky links)
  • BYOK multi-model AI consensus (Claude, Gemini, OpenAI, Grok, Ollama)

Team

Shared sender intelligence & M365 support for teams.

$19 / seat / mo

5-seat minimum · billed monthly

  • Everything in Individual for every seat
  • Microsoft 365 & Outlook Web Graph verification
  • Shared team first-contact sender history
  • One-click security team report forwarding
  • Multi-seat license management & priority support

Business & Enterprise · 25+ seats

Organization & VIP executive impersonation policies, custom allow/block lists, offline PO licensing, MSP rollouts, and custom MSA / DPA terms. Self-serve from $35/seat/mo ($29/seat/mo annual) or request an invoice quote.

Contact sales

Checkout is processed securely via Stripe, and your TSL1 license key is delivered by email immediately after purchase. Already subscribed? Manage your subscription or download invoices.

Quickstart

Deploy in under two minutes.

Install the browser extension, connect your AI client, or run both with the same license key.

Option 01 · Webmail

Chrome, Edge & Brave Extension

Open Gmail or Outlook on the web after installing. Protection starts immediately on the Free tier; paste your TSL1 key in Settings → License anytime to unlock unlimited scans, live domain intelligence, and Compose Guard.

Chrome Web Store — pending store review Compare plans
Option 02 · AI Agents (Node.js 20+)

MCP Server & Guarded Mailbox

Run one command to configure Claude Desktop, Claude Code, Cursor, or Windsurf. Pass --license-key or set TS_LICENSE_KEY to unlock Guarded Mailbox tools.

npx @threadscanner/mcp setup
Enterprise & Partnerships

Rolling out to a larger team or MSP client base?

Tell us about your environment for volume pricing, purchase-order invoicing, custom VIP impersonation policies, or a security architecture review.

  • 25+ seat Business & Enterprise volume licensing
  • Annual invoice / PO billing and offline air-gapped tokens
  • Signed DPA, sub-processor documentation, and MSA review
  • MSP & security consultancy partner deployments

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