BounceLens Email Check

BounceLens Email Check – MCP server

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

• Typos in the domain: [email protected] → did you mean [email protected]?
• 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. Setup guide for every client: bouncelens.com/mcp. 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"]
    }
  }
}

Grok Build

This repo is also a Grok Build plugin (.grok-plugin/plugin.json, .mcp.json and a skill in skills/). Install it from the plugin marketplace, or add the MCP server by hand with the same npx command as above.

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

Tool	Input	Returns
check_email	email (string)	One result
check_emails	emails (array, max 500)	summary with counts + one result per address, in input order

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

{
  "input": "[email protected]",
  "email": "[email protected]",
  "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": "[email protected]",
  "provider": null,
  "mx": null
}

status	Meaning
invalid	Will bounce: bad syntax, domain doesn't exist, no mail server, or null MX
risky	Disposable domain, likely typo, no MX record (mail would go to the web server), or the DNS lookup failed
unconfirmed	Format and domain OK. The mailbox itself isn't checked

Example prompts

• "Check these sign-ups for fake or mistyped emails: …"
• "Is [email protected] 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
• Google Sheets add-on – check a column of emails inside Google Sheets
• n8n node and WordPress plugin – the same checks in workflows and forms

License

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