---
title: "Email APIs - SMTP & RESTful API | OutboundSMTP"
description: "Two powerful integration paths: SMTP API with custom headers and category tagging, or RESTful API for email sending, subaccount management, domain configuration, and analytics."
image: "https://outboundsmtp.com/images/og-default.png"
canonical: "https://outboundsmtp.com/features/api/"
---

# Two Powerful Paths to Email Integration 

Whether you prefer traditional SMTP with enhanced headers or a modern RESTful API, OutboundSMTP has you covered.

[ Try 1000 Free Credits → ](https://insight.iljmp.com/4/smtp-free) [Read the API docs ↗ ](https://api.outbound.mailhop.org) 

SMTP API 

## Enhanced SMTP with custom headers

Use standard SMTP with our custom X-Headers to unlock advanced features without changing your sending infrastructure.

### Custom X-Headers

Add metadata to your emails using custom X-Headers. Track campaigns, set priorities, and control delivery behavior through SMTP headers.

### Category Tagging

Organize your email streams with category tags. Separate transactional from marketing email and track performance independently.

### Template Variables

Use merge tags in your SMTP messages for personalization. Dynamically replace variables at send time without pre-processing.

### Delivery Options

Control delivery timing, set send windows, configure retry policies, and manage bounce handling all through SMTP headers.

smtp-headers.txt 

```
# SMTP with Custom X-Headers
X-OSMTP-Category: transactional
X-OSMTP-Campaign: welcome-series
X-OSMTP-Template: onboarding-v2
X-OSMTP-Priority: high
X-OSMTP-Track-Opens: true
X-OSMTP-Track-Clicks: true

# Standard SMTP connection
Host: smtp.outboundsmtp.com
Port: 587
Auth: your-api-key
TLS: required
```

RESTful API 

## Modern API for full platform control

Our RESTful API gives you programmatic access to every feature of the OutboundSMTP platform.

### Email Sending

Send single or batch emails via API with full control over headers, attachments, templates, and delivery options.

### Subaccount Management

Create, update, and manage sub-accounts programmatically. Set limits, configure domains, and monitor usage via API.

### Domain Configuration

Manage sending domains, authentication records, and custom MAIL FROM settings through the API.

### Analytics & Reporting

Pull delivery reports, bounce data, engagement metrics, and aggregate statistics programmatically for custom dashboards.

send-email.sh 

```
# Send email via RESTful API
curl -X POST https://api.outbound.mailhop.org/v1/email/send \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "sender@yourdomain.com",
    "to": ["recipient@example.com"],
    "subject": "Hello from OutboundSMTP",
    "html": "

[Welcome!]

",
    "category": "transactional",
    "track_opens": true,
    "track_clicks": true
  }'
```

Regional endpoints 

## Point your client at the region closest to your sending profile

The API is region-aware. Use the base URL below your code lives nearest to. Authentication uses your existing Outbound SMTP credentials, the same ones you use on port 25 or 587.

US · Oregon 

`https://api.outbound.us.mailhop.org/` 

North America and Latin America customers, or anyone whose application servers run in AWS us-west, Azure West US, or GCP us-west regions.

EU · Frankfurt 

`https://api.outbound.eu.mailhop.org/` 

EU, UK, Middle East and Africa customers, or anyone with data-residency requirements that keep mail processing inside the EU.

Not sure which endpoint to pick, or need to route by region in code?

[Full API documentation ↗ ](https://api.outbound.mailhop.org) 

Integration Support 

## Everything you need to integrate

### Documentation

Comprehensive API reference with examples, guides, and tutorials to get you sending in minutes.

### SDKs

Official SDKs for JavaScript, Python, PHP, Ruby, Java, and .NET. Drop-in libraries for your preferred language.

### Sandbox Environment

Test your integration without sending real emails. Validate payloads, test error handling, and verify webhook processing.

### API Keys

Generate and manage API keys per sub-account. Rotate keys, set permissions, and track usage independently.

FAQ 

## Common API questions

### Can I use both SMTP and the RESTful API at the same time?

Yes. Both integration methods use the same account and share your sending credits. Many customers use SMTP for their application email and the RESTful API for management and analytics.

### What are the API rate limits?

Rate limits depend on your plan. All plans support burst sending, and dedicated IP plans include higher sustained throughput. Contact us for specific rate limit details for your use case.

### Do you offer webhooks for delivery events?

Yes. Configure webhook endpoints to receive real-time notifications for delivery, bounce, open, click, and complaint events. Webhooks support retry logic and signature verification.

## Start integrating today

Get 1,000 free email credits and full API access. No credit card required.

[Try 1000 Free Credits→](https://insight.iljmp.com/4/smtp-free)[Schedule a Demo](/contact-us/)

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```

```json
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```

```json
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```