MailCheck MCP

Stop your cold emails from landing in spam — right inside Claude, Cursor, or any MCP client.

MailCheck MCP gives your AI assistant two tools:

• check_domain — SPF / DKIM / DMARC / MX health for any sending domain, scored 0–4.

• check_copy — scans email subject+body for spam-trigger phrases, ALL-CAPS, and punctuation abuse, with a risk score.

Ask Claude "is my domain set up to send cold email?" or "will this email hit spam?" and get a real answer backed by live DNS lookups — no SaaS signup, no API key, no data leaving your machine.

Why

Cold email silently dies in spam folders when auth (SPF/DKIM/DMARC) is misconfigured or the copy trips spam filters. We built this after our own 300-email campaign got 0 replies — turned out to be an auth/offer problem we couldn't see. Now you can see it before you hit send.

Related MCP server: Email Verifier MCP

Install

Requires Node ≥ 18 and Python 3 (used for the DNS/dig logic), plus dig (standard on macOS/Linux). No signup, no API key — nothing leaves your machine.

Fastest — one line, no clone, no npm account

{
  "mcpServers": {
    "mailcheck": {
      "command": "npx",
      "args": ["-y", "github:myselfz3ro/mailcheck-mcp"]
    }
  }
}

Drop that into your MCP client's config and restart. npx fetches and runs it directly from GitHub — that's the whole install.

Or clone it

git clone https://github.com/myselfz3ro/mailcheck-mcp
cd mailcheck-mcp
npm run smoke   # verify it works

Claude Desktop

Add the npx block above to claude_desktop_config.json (or, if cloned, point command: "node" at /absolute/path/to/mailcheck-mcp/mcp/server.js).

Cursor / Windsurf / Zed

Point your MCP server config at node /absolute/path/to/mailcheck-mcp/mcp/server.js over stdio.

Tools

Note on DKIM

DKIM selectors are provider-specific. If you send through Gmail/Google Workspace SMTP, Google signs your mail with its own key — a selector probe on your domain will report "not found" even though your mail is signed. In that case, trust an inbox-placement test over the selector check.

License

MIT. Free. Tips welcome — PayPal · star the repo if it saved you from the spam folder.