# PostStack

> European email API platform for developers and AI agents. Send transactional and marketing emails via REST API, SMTP, or MCP server. EU-hosted infrastructure in Finland. 3,000 emails free every month, paid plans from €5.

PostStack is a Danish company. All data is processed and stored in the EU. GDPR compliant by design.

## Docs

- [Full API Reference](https://poststack.dev/llms-full.txt): Complete API documentation with all endpoints, schemas, and examples
- [OpenAPI 3.1 Spec](https://poststack.dev/openapi.json): Machine-readable API schema
- [Web Docs](https://poststack.dev/docs): Interactive documentation
- [MCP Server](https://poststack.dev/docs/mcp): Model Context Protocol server for AI assistants
- [MCP Discovery](https://poststack.dev/.well-known/mcp.json): Hosted MCP manifest (transport URL, auth methods, scopes)

## Quick Start

Install the SDK:

```bash
npm install @poststack.dev/sdk
```

Send your first email:

```typescript
import { PostStack } from '@poststack.dev/sdk';

const poststack = new PostStack('sk_live_...');

await poststack.emails.send({
  from: 'you@yourdomain.com',
  to: ['user@example.com'],
  subject: 'Hello',
  html: '<p>Welcome!</p>',
});
```

## MCP Server (AI Agents)

Connect PostStack to Claude, Cursor, Windsurf, and other AI assistants:

```bash
claude mcp add poststack -e POSTSTACK_API_KEY=sk_live_... -- npx -y @poststack.dev/mcp
```

72 tools covering the full API surface — send emails, manage contacts, domains, templates, broadcasts, and more via natural language.

## API Sections

- **Authentication**: Bearer token auth with API keys (`sk_live_...` or `sk_test_...`)
- **Emails**: Send single/batch emails, schedule, cancel, list with filtering
- **Domains**: Add and verify sending domains (SPF, DKIM, DMARC), configure tracking
- **Contacts**: Create, import (CSV), export, manage subscribers with custom properties
- **Templates**: Reusable email templates with `{{variable}}` placeholders and versioning
- **Broadcasts**: Bulk email campaigns to segments/topics with scheduling and analytics
- **Segments**: Dynamic (rule-based) and manual audience segmentation
- **Subscription Topics**: Fine-grained email preference management per contact
- **Workflows**: Automated email sequences triggered by contact events
- **Tracking**: Open and click tracking with custom domains, client/location detection
- **Inbound Email**: Receive emails via MX records and webhook notifications
- **Webhooks**: Real-time event notifications with signature verification
- **SMTP Relay**: Send via standard SMTP (port 587/465) using API key as password
- **Mailboxes**: Full email hosting with IMAP, POP3, and webmail at https://mail.poststack.dev (mailbox users sign in with their own address and password; they can also connect t-online, GMX, WEB.DE and other IMAP accounts)
- **Test Mode**: Use `sk_test_` keys for development — full validation, no delivery
- **SDK Reference**: TypeScript SDK with typed methods for all resources
- **Errors**: HTTP status codes, common error messages, and rate limiting

## Base URL

```
https://api.poststack.dev
```

## Authentication

All API requests require a Bearer token:

```
Authorization: Bearer sk_live_...
```

Two permission levels: `full_access` (all operations) and `sending_access` (send only).

## SDK Resources

```
poststack.emails        — send, list, get, cancel
poststack.domains       — create, list, get, verify, update, delete
poststack.contacts      — create, list, get, update, delete, import, export
poststack.templates     — create, list, get, update, delete, publish, duplicate
poststack.webhooks      — create, list, update, delete, test
poststack.broadcasts    — create, list, get, send, test, cancel
poststack.segments      — create, list, get, preview, addContacts, removeContacts, delete
poststack.subscriptionTopics — create, list, update, delete, subscribe, unsubscribe
poststack.inboundEmails — list, get
poststack.workflows     — create, list, get, activate, pause, delete
```

## Pricing

- **Free**: €0/mo — 3,000 emails, 1 domain
- **Starter**: €5/mo — 10,000 emails, 3 domains
- **Pro**: €15/mo — 50,000 emails, 10 domains, 30-day log retention
- **Scale**: €30/mo — 100,000 emails, 1,000 domains, 90-day log retention
- **Enterprise**: Custom pricing

Add-ons (any paid plan): hosted mailboxes €1/mo each (no count limit; each includes 1 GB, extra storage €1/GB/mo up to 50 GB), dedicated IP €25/mo (up to 1).
Overage: €0.25 per 1,000 emails on paid plans.

## Framework Guides

Copy-paste guides for sending transactional email with the PostStack SDK or SMTP from each stack.

- [Send email with Next.js](https://poststack.dev/docs/send-with-nextjs): Server actions and route handlers with the PostStack SDK.
- [Send email with Bun](https://poststack.dev/docs/send-with-bun): Native fetch and the SDK from a Bun server.
- [Send email with Express](https://poststack.dev/docs/send-with-express): Node.js route handlers, background jobs, and webhook verification.
- [Send email with Hono](https://poststack.dev/docs/send-with-hono): Edge and Node runtimes.
- [Send email with NestJS](https://poststack.dev/docs/send-with-nestjs): The SDK as an injectable provider, a MailService, and queued sends.
- [Send email with Nuxt](https://poststack.dev/docs/send-with-nuxt): Nitro server routes with runtimeConfig secrets.
- [Send email with SvelteKit](https://poststack.dev/docs/send-with-sveltekit): Form actions and +server.ts endpoints with a server-only client.
- [Send email with Python](https://poststack.dev/docs/send-with-python): Sync and async sends with the Python SDK.
- [Send email with Django](https://poststack.dev/docs/send-with-django): The SDK, or a drop-in EMAIL_BACKEND for send_mail, EmailMessage, EmailMultiAlternatives, and attachments.
- [Send email with Flask](https://poststack.dev/docs/send-with-flask): App-factory setup, background jobs, or Flask-Mail over SMTP.
- [Send email with FastAPI](https://poststack.dev/docs/send-with-fastapi): Async sends with BackgroundTasks.
- [Send email with Go](https://poststack.dev/docs/send-with-go): net/http client and the Go SDK.
- [Send email with Ruby on Rails](https://poststack.dev/docs/send-with-ruby): Net::HTTP or ActionMailer SMTP delivery.
- [Send email with PHP](https://poststack.dev/docs/send-with-php): cURL against the REST API, Symfony Mailer over SMTP, and WordPress.
- [Send email with Laravel](https://poststack.dev/docs/send-with-laravel): SMTP mailer in .env, Mailables, queued mail, notifications, and the Http client.
- [Send email with Java](https://poststack.dev/docs/send-with-java): JavaMail/SMTP and the REST API.
- [Send email with Spring Boot](https://poststack.dev/docs/send-with-spring): spring-boot-starter-mail with JavaMailSender over SMTP, or RestClient against the REST API.
- [Send email with Elixir](https://poststack.dev/docs/send-with-elixir): Swoosh and Bamboo SMTP adapters.
- [Send HTML email with Rust](https://poststack.dev/docs/send-with-rust): reqwest client and the REST API.

## Articles

Long-form guides written by the PostStack founder.

- [How to Set Up SPF, DKIM and DMARC for Your Sending Domain](https://poststack.dev/blog/spf-dkim-dmarc-setup-guide): Exact record examples, alignment, the 10-lookup limit, and how to verify with dig.
- [Why Are My Emails Going to Spam? A Developer's Checklist](https://poststack.dev/blog/why-emails-go-to-spam): Authentication, reputation, list hygiene, one-click unsubscribe, and reading Authentication-Results headers.
- [How to Choose a Transactional Email API: A Checklist](https://poststack.dev/blog/choose-transactional-email-api-checklist): Vendor-neutral criteria: data residency, deliverability tooling, webhooks, idempotency, pricing model, inbound, and SDKs.
- [Email Bounce Handling with Webhooks](https://poststack.dev/blog/email-bounce-handling-webhooks): Processing bounce and complaint events and keeping a suppression list in sync.
- [Automate SPF, DKIM, and DMARC with HostStack DNS](https://poststack.dev/blog/automate-spf-dkim-dmarc-with-hoststack-dns): Skip the copy-paste loop on every new sending domain. The integration publishes SPF, DKIM, DMARC, and return-path records into your HostStack zone and verifies via authoritative-server polling in 8-30 seconds.
- [Running an Email API on Managed Postgres: How PostStack Uses HostStack](https://poststack.dev/blog/email-api-on-managed-postgres-hoststack): Engineering story of moving PostStack's OLTP layer from bare-metal Postgres to HostStack-managed Postgres 18. What stayed self-managed (Postfix, Dovecot, Rspamd, workers), what the bill works out to, what the migration actually looked like.
- [The EU Email Stack: Why Your DNS and Database Provider Matter Too](https://poststack.dev/blog/eu-email-stack-dns-database-residency): GDPR doesn't stop at the email row. Four places EU residency typically leaks (DNS, backups, object storage, ops tooling) and how an end-to-end EU stack closes them.
- [Self-Host Email vs Use an API: A Decision Framework](https://poststack.dev/blog/self-host-email-vs-api-2026): When self-hosting Postfix makes sense vs paying for an API. Five variables, two clear-win scenarios, and the hybrid pattern most teams converge on.
- [GDPR-Compliant Email API in 2026: A Buyer's Guide](https://poststack.dev/blog/gdpr-compliant-email-api-2026): What "GDPR-compliant" actually means in practice, the four traps US-hosted providers fall into (CLOUD Act, "GDPR-ready" defaults, tracking pixels, log retention), and a 9-question checklist.

## Use Cases

- [All use cases](https://poststack.dev/use-cases)
- [Transactional email](https://poststack.dev/use-cases/transactional-email): password resets, magic links, receipts
- [Newsletters](https://poststack.dev/use-cases/newsletters): broadcasts to segments, A/B tests, one-click unsubscribe
- [AI agents](https://poststack.dev/use-cases/ai-agents): send email from Claude, Cursor and other MCP clients
- [SaaS products](https://poststack.dev/use-cases/saas): onboarding workflows and per-customer sending domains
- [E-commerce](https://poststack.dev/use-cases/ecommerce): order confirmations, shipping and receipts
- [Business email](https://poststack.dev/use-cases/business-email): IMAP mailboxes on your own domain
- [GDPR-compliant email](https://poststack.dev/use-cases/gdpr-compliant-email): EU hosting, a DPA and no CLOUD Act

## Glossary

- [DKIM](https://poststack.dev/glossary/dkim)
- [SPF](https://poststack.dev/glossary/spf)
- [DMARC](https://poststack.dev/glossary/dmarc)
- [Hard bounce vs soft bounce](https://poststack.dev/glossary/hard-bounce-vs-soft-bounce)
- [Transactional vs marketing email](https://poststack.dev/glossary/transactional-vs-marketing-email)
- [Return-Path](https://poststack.dev/glossary/return-path)
- [MTA-STS](https://poststack.dev/glossary/mta-sts)
- [BIMI](https://poststack.dev/glossary/bimi)
- [Feedback loop](https://poststack.dev/glossary/feedback-loop)
- [Email warmup](https://poststack.dev/glossary/email-warmup)
- [One-click unsubscribe](https://poststack.dev/glossary/one-click-unsubscribe)