Deliverability Doctor

Remote MCP server: "Can my domain be email-spoofed?" answered from public DNS, graded, with concrete fixes. Connectable to Claude (custom connector) and ChatGPT (Apps SDK / MCP connector) — both speak MCP, one server serves both.

Tools

• check_email_security(domain) — SPF (incl. RFC 7208 multiple-record permerror and redirect= handling), DMARC (policy, rua, pct), MX, DKIM at 7 common selectors. Graded A–F report, fixes per finding, upsell line only when problems exist. Accepts bare domain, URL, or email address.
• compare_email_security(domains[2..5]) — comparison table with grades.

Design decisions

• Authless: reads public DNS only, stores nothing, takes nothing but a domain. Lowest possible connect friction; nothing sensitive to protect.
• DNS-over-HTTPS (Cloudflare → Google fallback): identical code runs on local Node and on Cloudflare Workers — no dns module dependency.
• Stateless streamable HTTP: fresh transport per request, no sessions; safe to scale, trivial for clients.
• NXDOMAIN is refused, not graded — "domain doesn't exist" ≠ "spoofable".
• Verified against known postures before first run: gmail.com (redirect= must not be flagged), n8n.io (must grade A on p=reject), missing-everything domain (must grade F), NXDOMAIN (must refuse).

Run

npm install
node server.js          # :8787/mcp

Quick public demo: cloudflared tunnel --url http://localhost:8787 → use https://<random>.trycloudflare.com/mcp as the connector URL.

Status 2026-08-23

• Local: end-to-end MCP verified (initialize / tools/list / tools/call).
• Public: live via quick tunnel, initialize verified from the public URL.
• Durable hosting: pending — Cloudflare Workers deploy needs Kacper's account (~5 min). Tunnel URL dies with the process/PC.
• Directory submissions (Anthropic connector directory, ChatGPT apps): need the durable URL first, then Kacper's developer accounts.

Monetization path

Free tool = distribution. Report links the $99 written audit (niekonieczny.gumroad.com/l/vscjt) only when problems are found. NOTE: Gumroad payouts currently frozen on Stripe KYC — unfreeze before promoting.