BounceLens Email Check – MCP server

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Lets Claude, Cursor and other MCP clients check email addresses before you send to them or save them. It finds:

• Typos in the domain: jane@gmial.com → did you mean jane@gmail.com?
• Disposable / throwaway domains (mailinator.com, 10minutemail and ~9,000 more)
• Dead domains: the domain doesn't exist, has no mail server, or says it accepts no email (null MX)
• Bad syntax, role addresses (info@, sales@), free providers, and duplicates (Gmail dot and +tag variants count as the same inbox)
• The mail provider behind the domain (Google, Microsoft, Proofpoint, …)

Runs on your machine. No API key, no account, no sign-up. The only network calls are DNS lookups over HTTPS (Cloudflare 1.1.1.1). It uses the same checks as the free checker at bouncelens.com.

It never connects to the recipient's mail server, so it can't confirm that a mailbox exists. The best result is unconfirmed (format and domain OK). To check a whole CSV in your browser, use bouncelens.com.

Install

Requires Node.js 18 or newer. Also listed on Smithery.

Claude Code

claude mcp add bouncelens -- npx -y github:bouncelens/mcp-email-check

Claude Desktop, Cursor, Windsurf and other clients. Add this to the client's MCP config (claude_desktop_config.json, .cursor/mcp.json, …):

{
  "mcpServers": {
    "bouncelens": {
      "command": "npx",
      "args": ["-y", "github:bouncelens/mcp-email-check"]
    }
  }
}

From a clone

git clone https://github.com/bouncelens/mcp-email-check.git
cd mcp-email-check && npm install
# then use: "command": "node", "args": ["/path/to/mcp-email-check/index.js"]

Tools

Each result (real output for a mistyped Outlook address):

{
  "input": "jane@outlok.com",
  "email": "jane@outlok.com",
  "status": "risky",
  "reasons": ["No MX record; mail would go to the website server", "Looks like a typo of outlook.com"],
  "flags": { "disposable": false, "role": false, "free": false, "duplicate": false, "gateway": false },
  "did_you_mean": "jane@outlook.com",
  "provider": null,
  "mx": null
}

Example prompts

• "Check these sign-ups for fake or mistyped emails: …"
• "Is jane@outlok.com a real address?"
• "Clean this list: drop invalid and disposable addresses, fix the typos, remove duplicates."

Privacy

Addresses never leave your machine. Only the domain part is sent to Cloudflare's DNS-over-HTTPS resolver (1.1.1.1) to look up its MX/A records.

Development

npm install
npm test          # offline: DNS answers are faked

lib/engine.js and data/disposable.json are generated from the BounceLens main codebase, so change them there.

More from BounceLens

• bouncelens.com – free email list checker in your browser (CSV in, clean list out)
• Craft CMS plugin – blocks fake and mistyped emails in Craft forms

License

MIT. Disposable-domain list: disposable-email-domains (CC0).