SendMerlin: Shipping an Email Platform Solo

Email marketing tools charge by list size and hide deliverability behind support tickets. I wanted my own multi-tenant platform on AWS SES: campaigns, audiences, GDPR double opt-in and a sending pipeline I can reason about, priced flat. The hard part is the pipeline itself. Sending thousands of emails is easy; pausing on a bounce spike at 3 a.m. without human intervention is the product.

SendMerlin is Next.js 16 with a PostgreSQL send queue, no Redis. A separate worker claims batches with SKIP LOCKED, an atomic launch gate prevents double sends, and stale jobs re-queue themselves. The composer is GrapesJS over MJML, compiled server-side to email-safe HTML.

• Reputation ramp starting at 50 sends per day, doubling to the plan ceiling
• Auto-pause on bounce and complaint thresholds, with superadmin alerts
• RFC 8058 one-click unsubscribe headers on every send
• Per-client SES domain provisioning: DKIM, MAIL FROM, DMARC and tracking

The pipeline shipped with 222 unit tests across 38 files and 32 end-to-end tests, all green. A real worker drained a 480-recipient smoke campaign without a single miss, and the first live send landed on 16 July 2026. The platform now runs as two services from one Docker image: web and worker.