day3 MCP server

Day3

Marketing and transactional email, billed by sends. $1/mo. No contact tax, no marketing suite to learn.

day3.app

Source-available, not open source. This code is published for

transparency and reference. See LICENSE for terms.

This repository is the Day3 product itself: the app at go.day3.app, the public REST API, the webhook and MCP endpoints, and the worker that sends the mail.

What it does

Day3 is a deliberately small email tool for small SaaS teams. Send product updates and changelogs to your users, and send your app's transactional email (password resets, receipts, magic links), through one verified domain, one monthly allowance, and one place to see delivery.

per-send stats

• Campaigns with a block composer, optional AI assist, scheduling, and

categories), CSV import, and hosted signup forms

• Audiences with segments (saved filters), topics (subscription

with per-email delivery status

• Transactional email over POST /v1/emails, Resend-compatible in shape,

published as immutable versions, unlimited on every tier

• Automations: onboarding and lifecycle flows drawn on a node canvas,

one-click unsubscribe, automatic bounce and complaint suppression, account auto-pause on bad reputation

• Deliverability by default: verified sending domains, double opt-in,

log of every email you ever sent

• Metrics for deliverability, reputation and engagement, plus a searchable

Cursor or VS Code can draft a campaign that lands in Day3 as editable blocks

• Public API v1, signed webhooks, and an MCP server so Claude Code,

audiences and send for real in sandbox mode. Paid plans buy the allowance to reach everyone else.

• Billed on sends, not subscribers. Free accounts set up domains, build

PRODUCT.md is the canonical description of what Day3 is, what it costs, and how every feature behaves. Read it before the code.

Tech stack

Quick Links

Built by Pradsgaard Labs. Also from the same workshop: exit1.dev, uptime monitoring.

Local development

npm install

# Env: web tier + worker (see "Required environment variables" below)
cp .env.example .env.local
cp .env.worker.example .env.worker

# Database
npm run db:migrate     # forward-only, applies un-applied journal entries
npm run db:seed        # optional sample data

npm run dev            # Next.js on http://localhost:3000
npm run worker         # BullMQ worker, in a second terminal

Shortened. The full README is on GitHub.