> ## Documentation Index
> Fetch the complete documentation index at: https://developers.effilink.co/llms.txt
> Use this file to discover all available pages before exploring further.

# Overview

***

## title: "EffiLink REST API: Cloud Messaging for Email and SMS" sidebarTitle: "Overview" description: "EffiLink is a cloud messaging REST API for sending transactional email, marketing campaigns, and SMS with real-time delivery tracking and webhooks."

EffiLink gives you a single REST API to send transactional emails, run marketing campaigns, deliver SMS messages, and receive real-time engagement events via webhooks. All of this runs on EffiLink's infrastructure at `api.effilink.co`, so you focus on your product, not on deliverability.

## What you can do with EffiLink

<CardGroup cols={2}>
  <Card title="Transactional Email" icon="envelope" href="/docs/transactional-email">
    Send triggered emails like order confirmations, password resets, and shipping notifications.
  </Card>

  <Card title="Marketing Campaigns" icon="bullhorn" href="/docs/campaign-email">
    Create and deliver newsletters, promotions, and announcements to contact lists.
  </Card>

  <Card title="SMS" icon="mobile" href="/docs/sms-send">
    Send individual or bulk SMS messages for notifications and promotions.
  </Card>

  <Card title="Webhooks" icon="webhook" href="/docs/webhooks">
    Receive real-time events for every delivery, open, click, bounce, and unsubscribe.
  </Card>
</CardGroup>

## API fundamentals

EffiLink provides geographically distributed API endpoints to ensure high availability and optimal access performance. Please use the endpoint closest to your application's deployment region:

\- Mainland China:

```text theme={null}
https://api.effilink.co
```

\- Hong Kong China:

```text theme={null}
https://hk-api.effilink.co
```

\- Europe:

```text theme={null}
https://eu-api.effilink.co 
```

For the best latency and reliability, we recommend selecting the endpoint that is geographically closest to your users or application servers.

Every request must:

\- Be sent over **HTTPS**
\- Use `Content-Type: application/json`
\- Include an authentication header (`ApiKey` or `OAuth`)

<Note>
  Parameter names are **case-sensitive**. All request and response data uses UTF-8 encoding.
</Note>

## HTTP response codes

| Code | Status | Meaning |
| - | - | - |
| 200 | OK | Request succeeded |
| 400 | Bad Request | Invalid data format or missing required parameter |
| 404 | Not Found | Endpoint does not exist |
| 405 | Method Not Allowed | Use GET or POST as specified |
| 429 | Too Many Requests | Rate limit exceeded |
| | | |

## Pagination

List and search endpoints return paginated results. Use these query parameters to navigate pages:

| Parameter | Type | Description |
| - | - | - |
| `pageSize` | integer | Number of records per page |
| `pageIndex` | integer | Page number, starting from `1` |

## Next steps

<CardGroup cols={2}>
  <Card title="Quick Start" icon="rocket" href="/docs/quickstart">
    Send your first email in under 5 minutes.
  </Card>

  <Card title="Authentication" icon="key" href="/docs/authentication">
    Learn how to authenticate API requests.
  </Card>
</CardGroup>


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