MailCred — Deliverability Pre-Flight Checker for Transactional Email Senders
You built a beautiful onboarding email sequence and it lands in spam for 40% of your users. MailCred runs your transactional email through a live deliverability gauntlet before you hit send — SPF, DKIM, DMARC, blacklist checks, and inbox placement prediction in 90 seconds.
Difficulty
intermediate
Category
Developer Tools
Market Demand
High
Revenue Score
7/10
Platform
Web App
Vibe Code Friendly
⚡ YesHackathon Score
🏆 7/10
Validated by Real Pain
— sourced from real community discussions
Developers building email-sending tools need legitimate deliverability infrastructure and currently cobble together multiple DNS lookup sites and manual checks with no unified workflow.
What is it?
Every SaaS founder sending transactional email via Resend, SendGrid, or Postmark eventually discovers their emails are silently rotting in spam folders. Diagnosing this requires seven different tools, three DNS lookup sites, and a Stack Overflow tab. MailCred collapses the entire deliverability audit into one API call or web UI paste. Paste your raw email headers or connect your sending domain, and get a scored report covering SPF alignment, DKIM signature validity, DMARC policy enforcement, MX record health, major blacklist presence, and a heuristic inbox placement score. Target is legitimate SaaS teams and indie hackers — not spam operators. Buildable in two weeks using public DNS lookup APIs, MXToolbox-style record parsing, and Claude for plain-English report generation.
Why now?
Resend crossed 100k developer users in 2025 and the transactional email space is exploding — but deliverability tooling for indie hackers remains stuck in 2015 UX. Claude API makes the fix-instruction layer trivially cheap to add.
- ▸Paste raw email headers or enter sending domain for instant audit (Implementation note: node:dns + mailauth for record parsing)
- ▸Scored deliverability report across SPF, DKIM, DMARC, and blacklists
- ▸Claude-generated plain-English fix instructions per failed check
- ▸Domain monitoring mode that alerts via email when records drift
Target Audience
SaaS founders and indie hackers sending transactional email, estimated 200,000+ Resend and SendGrid users globally.
Example Use Case
Priya launches her SaaS and pastes her welcome email headers into MailCred, discovers her DKIM is misconfigured on her subdomain, fixes it in 10 minutes using the plain-English instructions MailCred generates, and her onboarding completion rate jumps 18% the next week.
User Stories
- ▸As a SaaS founder, I want to paste my email headers and get a pass or fail score in 90 seconds, so that I know if my onboarding emails are reaching inboxes.
- ▸As a developer, I want plain-English fix instructions for each failed check, so that I can resolve DKIM issues without reading an RFC.
- ▸As a team lead, I want continuous domain monitoring with Slack alerts, so that I know the moment our email configuration drifts.
Done When
- ✓Header check: done when user pastes raw headers and sees a scored report with green or red status per check within 5 seconds.
- ✓AI fix: done when each failed check shows a collapsible plain-English fix block generated by Claude.
- ✓Free limit: done when user hits 3 checks and sees an upgrade prompt before the fourth check runs.
- ✓Monitoring: done when user adds a domain and receives an email alert within 1 hour of a simulated record change.
Is it worth building?
$19/month x 80 solo devs = $1,520 MRR at month 3. $49/month team plan x 60 teams = $2,940 MRR at month 5.
Unit Economics
CAC: $8 via community posting. LTV: $228 (12 months at $19/month). Payback: 1 month. Gross margin: 85%.
Business Model
Freemium with usage-based paid tier
Monetization Path
Free for 3 checks per month. Paid at $19/month for unlimited checks and domain monitoring. Team plan at $49/month adds API access.
Revenue Timeline
First dollar: week 3 via first paid upgrade. $1k MRR: month 3. $5k MRR: month 8.
Estimated Monthly Cost
Claude API: $30, Vercel: $20, Supabase: $25, blacklist API: $15, Stripe fees: $10. Total: $100/month at launch.
Profit Potential
Part-time income at $3k MRR, full-time viable at $8k MRR.
Scalability
High — add continuous domain monitoring, team seat billing, Slack alerting, and white-label for email agencies.
Success Metrics
Week 2: 200 free checks run. Month 2: 40 paid users. Month 3: 85% monthly retention.
Launch & Validation Plan
Post a free tool on r/selfhosted and r/webdev, collect 100 email checks, see how many hit the free limit and ask about paid.
Customer Acquisition Strategy
First customer: post the free checker in r/SaaS and r/indiehackers with a screenshot of a real failing DKIM report. Then: ProductHunt launch, Resend community Discord, Twitter SEO thread on email deliverability.
What's the competition?
Competition Level
Medium
Similar Products
MXToolbox is comprehensive but requires DNS expertise to interpret. Mail-tester.com requires sending a live email. Google Postmaster Tools only works for Gmail — none offer AI-generated fix instructions.
Competitive Advantage
MXToolbox requires knowing what to look for. Mail-tester requires sending a real test email. MailCred works by pasting headers and speaks plain English — uniquely frictionless for non-DNS-expert founders.
Regulatory Risks
Low regulatory risk. No email content is stored. Only DNS records and header metadata processed.
What's the roadmap?
Feature Roadmap
V1 (launch): header paste, DNS audit, AI fix instructions, Stripe paywall. V2 (month 2-3): domain monitoring, Slack alerts, check history. V3 (month 4+): API access, team seats, white-label for email agencies.
Milestone Plan
Phase 1 (Week 1-2): DNS parsing, report UI, Claude fix generation live. Phase 2 (Week 3-4): Stripe billing, monitoring cron, deploy. Phase 3 (Month 2): 40 paid users, ProductHunt launch.
How do you build it?
Tech Stack
Next.js, Claude API, Resend, Supabase, Node DNS module — build with Cursor for DNS parsing logic, v0 for report UI components.
Suggested Frameworks
node:dns, mailauth npm package, Claude API
Time to Ship
2 weeks
Required Skills
DNS record parsing, Next.js API routes, Claude API for report generation, Stripe billing.
Resources
mailauth npm docs, MXToolbox API reference, Resend docs, Claude API docs.
MVP Scope
app/page.tsx (landing + paste input), app/report/[id]/page.tsx (scored report UI), app/api/check/route.ts (DNS + blacklist audit), app/api/monitor/route.ts (cron domain watcher), lib/parse.ts (mailauth wrapper), lib/db/schema.ts (Drizzle schema), components/ScoreCard.tsx (report card UI), components/FixBlock.tsx (Claude fix instructions), seed.ts (sample report), .env.example.
Core User Journey
Paste email headers -> click check -> view scored report -> read plain-English fix -> re-check to confirm pass.
Architecture Pattern
User pastes headers or domain -> API route parses with mailauth + node:dns -> blacklist API checked -> Claude generates fix text -> report stored in Supabase -> rendered on report page.
Data Model
User has many DomainChecks. DomainCheck has one Report. Report has many CheckItems. CheckItem has one AIFixSuggestion.
Integration Points
mailauth npm for DKIM and SPF parsing, node:dns for MX and TXT records, MXToolbox API or Spamhaus API for blacklists, Claude API for fix generation, Stripe for billing, Resend for alert emails.
V1 Scope Boundaries
V1 excludes: SMTP connection testing, inbox placement simulation, mobile app, team collaboration, API key access.
Success Definition
A solo founder pastes their email headers, gets a failing DKIM score, follows the Claude-generated fix steps, re-runs the check, and passes — all without googling anything.
Challenges
MXToolbox and mail-tester.com already exist for free — you must win on UX simplicity and the AI fix-instruction layer, not raw features. Distribution to indie hackers is fast but getting SaaS teams to pay requires trust signals.
Avoid These Pitfalls
Do not build monitoring before the single-check flow is validated by 50 real users. Do not try to compete with MXToolbox on feature breadth — win on clarity. Finding first 10 paying customers takes 3x longer than building — post the free tool publicly first.
Security Requirements
Supabase Auth with Google OAuth, RLS per user on all check data, rate limit 20 checks/hour per IP, headers never stored raw beyond report generation.
Infrastructure Plan
Vercel for Next.js and API routes, Supabase for Postgres, Vercel Cron for domain monitoring, Sentry for errors, Vercel Analytics for traffic. Total: $100/month.
Performance Targets
100 DAU at launch, 1,000 req/day. DNS audit API response under 3s. Report page load under 2s. No caching needed at launch scale.
Go-Live Checklist
- ☐Security audit complete.
- ☐Stripe payment flow tested.
- ☐Sentry error tracking live.
- ☐Monitoring dashboard configured.
- ☐Custom domain with SSL active.
- ☐Privacy policy and terms published.
- ☐10 beta users signed off.
- ☐Rollback plan documented.
- ☐Launch post drafted for ProductHunt and r/indiehackers.
First Run Experience
On first run: a pre-loaded demo report for a fictional domain 'demo-saas.com' with two failing checks and AI fix instructions is visible immediately. User can immediately interact with the report, expand fix blocks, and paste their own headers. No manual config required: demo report seeded, Stripe in test mode, Claude API connected.
How to build it, step by step
1. Define Drizzle schema: DomainCheck, Report, CheckItem, AIFix tables. 2. Run npx create-next-app with App Router and Tailwind. 3. Install mailauth and write lib/parse.ts wrapper for SPF, DKIM, DMARC extraction. 4. Add node:dns lookup for MX and TXT records in API route. 5. Integrate Spamhaus HTTP API for blacklist status. 6. Send parsed results to Claude API and prompt for plain-English fix per failed item. 7. Build ScoreCard and FixBlock components with v0. 8. Add Stripe Checkout for $19/month plan with usage gate at 3 free checks. 9. Seed one sample failing report as demo state on landing page. 10. Deploy to Vercel and walk the full journey: paste real headers, confirm report renders, click Stripe upgrade, verify limit lifts.
Generated
May 6, 2026
Model
claude-sonnet-4-6
Disclaimer: Ideas on this site are AI-generated and may contain inaccuracies. Revenue estimates, market demand figures, and financial projections are illustrative assumptions only — not financial advice. Do your own research before making any business or investment decisions. Technology availability, pricing, and market conditions change rapidly; always verify details independently.