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Rumblingb
Rumblingb

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I Built an Email Verification MCP Server in 24 Hours — Here's How

#mcp #email #devtools #buildinpublic

Why Email Verification?

Every time you build a SaaS product, a signup form, or a lead capture page, you face the same problem: fake emails.

Invalid emails waste your deliverability budget, pollute your CRM, and cost you money on third-party verification services. So I built my own.

What is an MCP Server?

MCP (Model Context Protocol) is Anthropic's open standard for connecting AI assistants to external tools. Think of it as USB-C for AI — one protocol that lets Claude, Hermes, or any MCP-compatible agent call your tools directly.

An MCP server is just a small HTTP + SSE service that exposes tools. No SDK lock-in. No vendor gatekeeping.

The Stack

  • Python + FastMCP — lightweight MCP server framework
  • SMTP check — verifies the mail server exists
  • DNS MX lookup — checks domain has mail records
  • Disposable domain list — catches temp mail addresses
  • npm package — @rumblingb/email-verify-mcp

How It Works 

@mcp.tool()
def verify_email(email: str) -> str:
    # 1. Regex format check
    # 2. DNS MX record lookup
    # 3. SMTP handshake (without sending)
    # 4. Disposable domain check
    return {"valid": True, "score": 0.92, "details": "..."}
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The server exposes a single verify_email tool. Any MCP client can call it with an email address and get back a verification score with detailed diagnostics.

The Numbers

  • Time to build: ~24 hours (including research + publishing)
  • npm downloads: 29/week (and growing)
  • Revenue: $7.00 from 1 sale (Stripe payment link)
  • Cost to run: $0 (serverless)

The Business Model

I put a Stripe payment link on the npm readme and the GitHub repo. The MCP server itself is open source (MIT), but the hosted version costs $1/99 verifications.

One customer in week one. The unit economics check out.

Why This Matters

This is the playbook for the AI agent tool economy:

  1. Build a useful MCP server
  2. Publish it on npm + GitHub
  3. Add a Stripe payment link
  4. Write about it on Dev.to
  5. Repeat

No VC funding. No team. No meetings. Just shipping.

Try It Yourself

  • npm: @rumblingb/email-verify-mcp
  • GitHub: github.com/Rumblingb/email-verify-mcp
  • Buy: buy.stripe.com/aFadRb2z56ZKaU00wz1oI1l

The code is MIT. Go fork it, improve it, and build your own.

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