Pre-send spam score with actionable fix suggestions

Overview

A pre-send "spam check + fix" tool and API: paste an email's HTML or plain text before sending and get a spam score, a list of the exact triggers, and concrete remediation steps (copy, links, images, SPF/DKIM/DMARC). Built for cold email operators, newsletter marketers and indie SaaS founders.

Pain Point

Existing free tools — and API products like Unspam — return a score and a pile of keyword hits. Users get "7.2/10" and still have no idea which sentence to rewrite, which link to drop, or how to change the subject line. So they keep resending variants, burning send quota and domain reputation with no improvement. Enterprise inbox-placement monitoring (seed-list tools) is expensive and is post-send monitoring, not pre-send repair.

Target User

• Cold email / outbound operators and small agencies
• Indie SaaS founders running their own lifecycle email
• Small ecommerce newsletter teams Persona: understands email marketing basics, has no dedicated deliverability engineer, sends 5k–200k emails per month.

Market Opportunity

The original signal points at an API-driven niche well suited to a solo builder; deliverability is tied directly to revenue, so failures cost real money. Competitors stop at scoring, which leaves a clear "score → fix" gap that a rules knowledge base plus modest engineering can fill.

Monetization

Inferred (no pricing clues in the source): freemium with 3 free checks per day for SEO and top-of-funnel; $19/mo for 500 checks with fix suggestions and history; $49/mo for unlimited API, bulk scanning and webhooks. Comparable to Mail Tester and GlockApps pricing bands, which indie marketers and small teams already pay.

Technical Complexity

Medium. The core is running a rules engine such as SpamAssassin in a container, plus SPF/DKIM/DMARC DNS validation, blocklist lookups (Spamhaus etc.), and link/image analysis. The real challenges are cold-start DNS latency and third-party rate limits, which require caching and an async job queue. Not doable purely client-side, but backend scope is manageable.

Competition

• Mail Tester: the long-standing free single-email checker; gives a score and report but no remediation, no API, and the product has barely evolved.
• GlockApps: enterprise inbox-placement monitoring via seed lists; expensive and post-send.
• Unspam: API-based spam scoring that stops at the number, with weak remediation.
• Postmark / Mailgun built-in spam checks: tied to their own sending infrastructure, not usable standalone. Entry barrier: low-medium. Rules engines and DNS checks are commodity; the moat is the accumulated remediation knowledge base and API ergonomics.

GTM Strategy

• Primary channel: SEO long-tail ("email spam checker", "why is my email going to spam", "spam score checker api") plus cold-email and indie hacker communities (r/emailmarketing, r/coldemail, Indie Hackers).
• Cold-start tactic: post in r/emailmarketing and r/coldemail offering to manually check 20 emails free with line-by-line fixes — this trades labor for seed users and real case studies. Follow with a free-tool launch on Product Hunt.
• Content leverage: strong. "Why your cold email lands in spam: 12 fixes", "SPF vs DKIM vs DMARC explained", "Mail Tester alternatives" are all high-volume long-tail angles.

Execution Plan

• MVP core features: (1) paste HTML/text → score plus trigger list; (2) each trigger paired with a specific fix and rewritten example; (3) SPF/DKIM/DMARC domain check. Cut inbox-placement monitoring and list cleaning.
• What NOT to build: seed-list inbox monitoring (requires maintaining many mailboxes), ESP integrations, multi-language UI.
• Tech stack suggestion: Next.js + Vercel frontend; Node/Fastify backend with containerized SpamAssassin and Redis cache; Stripe for billing; Upstash for API key metering.
• Estimated time to launch: medium, 4–6 weeks; a usable version in ~3 weeks if the SpamAssassin containerization goes smoothly.