Lead & Audit Tools·8h build·Credit Pack / Pay-Per-ListBlueprint idea

Email List Syntax & MX Checker

Upload a CSV of emails and flag bad syntax, domains with no mail server, common typos, role addresses and disposable domains before you send.

Economics

Pricing example: $9 per 10,000 emails checked (first 500 free)
Daily math: 2-3 packs a day x $9 = $18-27/day.
Target if you hit the daily math: Target: $550 - $800 / month if the daily math is hit

Audience and urgency

Audience: Small marketers, newsletter writers, event organisers and agencies cleaning lists they collected themselves before importing them into an email tool.

Urgency: Old or hand-typed lists contain typos, dead domains and throwaway addresses. Sending to them causes bounces, which can hurt deliverability for the whole account.

MVP scope

✓ Upload CSV/XLSX; detect the email column; remove exact and case-only duplicates
✓ Syntax check plus domain checks: domain resolves and has MX (or fallback A) records
✓ Typo suggestions for common domains (e.g. gmial.com to gmail.com) and role-address flags (info@, admin@, sales@)
✓ Disposable-domain flag using an openly licensed list (check the licence before shipping)
✓ Results with a status per row, filters and clean/flagged CSV exports; credits via Stripe

Omitted features

- Do NOT probe mailboxes over SMTP (RCPT TO); it is unreliable and can get your servers blocklisted
- Do NOT store, share or resell uploaded lists
- Do NOT build email sending

Suggested stack

Frontend: React + Tailwind CSS + Papa Parse
Backend or API: Serverless function for DNS lookups with a per-domain cache; Supabase for credits
Payments: Stripe Checkout (credit packs)
Hosting: Vercel or Netlify (free tier to start)

Repository metadata

Blueprint ID: email-list-mx-checker
Category ID: lead_scraper_tool
Monetization ID: usage_pack

Day-one distribution

Channels

Reddit r/emailmarketing and r/marketing (follow self-promotion rules)
Newsletter-writer communities
A free single-email checker page

Reddit strategy

Explain in plain terms what a syntax and MX check can and cannot tell you, and offer 500 free checks.

Cold outreach or directory hook

Offer event organisers a free clean of their attendee export before their follow-up email.

Search keywords

email list cleaner free, check email domain mx record, remove disposable emails from list

One-shot master prompt

Build an "Email List Checker" web app in React with Tailwind CSS and a serverless DNS function.
Core requirements:
1. Upload CSV/XLSX (Papa Parse/SheetJS), auto-detect the email column, trim and lowercase, and remove duplicates.
2. Client-side checks: syntax (a practical regex plus length limits), role-address list, typo suggestions for 20 common providers using edit distance, and disposable-domain matching from a bundled openly licensed list.
3. Server function: for each unique domain, resolve MX records (fallback to A/AAAA), cache results for 24 hours, max 20 lookups in parallel. Never connect to mail servers.
4. Results table with a status per row (valid-format, no-mail-server, disposable, role, typo-suggested, duplicate), filters, and exports for "clean" and "flagged" lists.
5. 500 free checks, then Stripe Checkout ($9 per 10,000). Uploaded data is processed in memory and never stored; say so in the UI. Explain that the tool cannot confirm a specific mailbox exists.

Comparable products

Published 2026-10-08.

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