I'm building an app and want a simple transactional email API with templates

A simple transactional email API with templates usually needs just a few pieces:

Core features

• Send email endpoint: POST /send
• Template management:
  • POST /templates
  • GET /templates/:id
  • PUT /templates/:id
• Variable substitution for things like {{firstName}}, {{orderId}}
• Queueing / async sending so requests return fast
• Delivery status tracking: queued, sent, failed, bounced
• API keys / auth
• Webhooks for delivery events
• Optional: attachments, HTML/text versions, locale support

Simple API shape

Example request:

POST /send
{
  "to": "user@example.com",
  "templateId": "welcome_email",
  "data": {
    "firstName": "Ava",
    "loginLink": "https://app.example.com/login"
  }
}

Example template:

<h1>Welcome, {{firstName}}!</h1>
<p>Log in here: <a href="{{loginLink}}">Login</a></p>

Recommended template engine

For simplicity:

• Handlebars
• Mustache
• Or a very small custom {{variable}} replacement system

Minimal architecture

• API server: receives send requests
• Template store: DB or file-based
• Render layer: merges data into template
• Mail provider: SES, SendGrid, Postmark, Mailgun, or SMTP
• Job queue: Redis + BullMQ / Sidekiq / Celery depending on stack

Best practice

If you want it to stay simple, start with:

1. One send endpoint
2. Stored templates with variables
3. Queue background sending
4. Webhook for status updates

If you want, I can help you design:

• a REST API spec
• a database schema
• a Node/Python implementation
• or a minimal MVP architecture