Postmark: Fast, Reliable Email Delivery Service | SMTP | API

# Postmark > Postmark is a reliable transactional and bulk email service that helps developers deliver and track application emails. It provides REST APIs, SMTP support, webhooks, and comprehensive email templates to replace traditional SMTP with a scalable, developer-friendly solution. ## Quick Start To use Postmark for sending emails in your application: 1. Create a Postmark account and verify your sending domain or email address 2. Get your Server API Token from your Postmark server settings 3. Use the REST API or SMTP to send emails 4. Maximum email size is 10 MB (including attachments) 5. Maximum 50 recipients per email (To, CC, BCC combined) ### Authentication All API requests require authentication using the `X-Postmark-Server-Token` header with your Server API Token: ``` X-Postmark-Server-Token: your-server-token-here ``` For testing without actually sending emails, use `POSTMARK_API_TEST` as your token. ## API Reference - [TypeScript transactional email recipe](https://postmarkapp.com/developer/integration/official-libraries#typescript): Install, shared client, template send, batch handling, webhook verification, and repair guide — complete TypeScript path from setup to production - [Send a receipt with templates](https://postmarkapp.com/developer/api/templates-api#send-a-receipt-with-templates): Task-first TypeScript examples for receipts, welcome emails, and other structured transactional sends using `TemplateAlias` and `TemplateModel` - [Webhook verification guide](https://postmarkapp.com/developer/webhooks/webhooks-overview#protecting-your-webhook): Node/TypeScript raw-body HMAC-SHA256 signature verification, event parsing, Express route setup, and idempotency pattern - [Batch send with partial-failure handling](https://postmarkapp.com/developer/user-guide/send-email-with-api/batch-emails): TypeScript `Promise.allSettled` batch example with per-recipient `MessageID` and error reporting - [Send a single email](https://postmarkapp.com/develope