TOOLING / DATA

A Free Email Verifier Built With Claude Code

Email verification results table across domains by SMTP and identity checks

Published by Nilesh Patil on LinkedIn on 17 March 2026. Reproduced here unchanged. Read the original on LinkedIn.

I built an email verification system yesterday using Claude Code. Open-source tools. Free APIs. $0 per verification.

Is it as polished as the paid tools? No. Is it 90% of the way there for $0? Yes.

I didn't set out to replace paid tools. They work well. But I wanted to understand what's under the hood. Turns out, email verification comes down to three things: SMTP probing, identity server lookups, and IP reputation. All three are replicable with open-source tools and public APIs.

I described the logic: classify domains first, then verify. Route different domain types to different methods. Handle edge cases like gateways and catch-all domains. Layer in a free Microsoft API that most people don't know exists.

Claude Code took that description and built the whole thing. Scripts, server setup, DNS configuration, batch processing.

A year ago, this would have been a two-week dev project. Now it's an afternoon or a weekend project.

That's what Claude Code makes possible. Not just for email verification. For any tool, you can describe it clearly enough.

Comment "open source" if you want the tech stack and SOP!