Drip

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Build me the behavioural email system that replaces Drip.

**Segmentation is the product, and segmentation is SQL.** That is the whole insight: what these platforms sell as a visual audience builder is a WHERE clause over events you already have.

STACK
- Node 20+ with Fastify
- SQLite through better-sqlite3, WAL mode
- A worker process
- MJML for templates, a relay for delivery
- Caddy in front

THE DATA MODEL
- contacts: id, email, consent_at, source, attrs_json, unsubscribed_at
- events: id, contact_id, name, props_json, at — viewed a product, added to cart, ordered, opened, clicked. **One table, and a new behaviour is a new name rather than a migration**
- segments: id, name, sql, refreshed_at — stored as a predicate, evaluated at query time
- campaigns and flows, with enrolments and sends as usual
- suppressions, permanent

SEGMENTS AS QUERIES
- A segment is a saved SQL predicate over contacts and events. Bought in the last ninety days; viewed a category three times and never bought; opened nothing in six months
- **Evaluate at send time, not on a schedule.** A segment computed last night sends to people who no longer belong in it, and 'we emailed a discount to somebody who bought yesterday' is exactly that bug
- Show the current count beside every segment, and a sample of ten members. A segment nobody can spot-check is a segment nobody trusts
- Keep a snapshot of who was in the segment at send time, so a campaign report is reproducible

BEHAVIOURAL TRACKING WITHOUT BEING CREEPY
- Track product views and cart actions from your own shop, first-party, no third-party script
- **Say what you track, on the site, in plain words.** A shop that emails somebody about a product they looked at once and did not buy needs to have been visibly honest about watching, or it reads as surveillance and it costs you the customer
- Never email about anything sensitive that was browsed. Have a category exclusion list and use it

THE FLOWS
- A queue with a lease, idempotency per contact per step, exit conditions checked before every step
- A global per-contact frequency cap across every flow and campaign
- Quiet hours in the contact's timezone

MEASURING WHAT IS TRUE
- Revenue attributed within a stated window, shown beside total revenue
- **A permanent holdout slice on every automated flow.** Without it, 'the abandoned cart flow earned this much' includes everybody who would have returned anyway
- Unsubscribe and complaint rate per flow, which is the cost side of the ledger and is usually hidden

LIST HYGIENE
- Stop sending to people with no engagement in six months. It improves delivery for everybody else and it is the cheapest lever there is
- Confirmed opt-in recorded with time and source; one-click unsubscribe on every message

WHAT MATTERS MOST
Segments evaluated at send time, and a holdout on every flow. One keeps the messages correct; the other keeps the reporting honest.