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

# Send a Single Transactional Email — EffiLink API

> Send a single personalized transactional email with optional scheduling, open/click tracking, file attachments, and saved template support.

## Overview

Send a single transactional email to one recipient. You can supply raw HTML content or reference a saved template, personalize the message with dynamic tags, schedule delivery up to 72 hours in advance, track opens and clicks, and attach a file — all in one request.

**Base URL:** `https://api.effilink.co`

**Endpoint:** `POST /v5/transactional/mail/sends_customised`

**Authentication:** `ApiKey` header

***

## Request Parameters

<ParamField body="subject" type="string" required>
  Email subject line.
</ParamField>

<ParamField body="content" type="string">
  HTML email body content. Required if `templateName` is not provided.
</ParamField>

<ParamField body="templateName" type="string">
  Name of an existing saved template. Takes priority over `content` when both are provided.
</ParamField>

<ParamField body="params" type="object">
  Key-value pairs used to populate personalization tags in the format `{{tagName}}` within your `content` or template.

  ```json theme={null}
  { "name": "Jane", "orderId": "ORD-5678" }
  ```
</ParamField>

<ParamField body="senderMail" type="string" required>
  Verified sender email address. Must be registered in your EffiLink account before use.
</ParamField>

<ParamField body="senderName" type="string">
  Sender display name shown in the recipient's inbox. Maximum **200 bytes**.
</ParamField>

<ParamField body="replyTo" type="string">
  Reply-to email address. Replies from recipients will be directed here instead of `senderMail`.
</ParamField>

<ParamField body="sendDate" type="string">
  Scheduled send time in ISO 8601 UTC format (e.g. `2024-03-10T12:00:00Z`). Schedule up to **72 hours** in advance. Omit this field to send immediately.
</ParamField>

<ParamField body="to" type="object" required>
  The single recipient of this email.

  <Expandable title="to fields">
    <ParamField body="to.email" type="string" required>
      Recipient email address.
    </ParamField>

    <ParamField body="to.name" type="string">
      Recipient display name.
    </ParamField>
  </Expandable>
</ParamField>

<ParamField body="category" type="string">
  Email category label for organizational and reporting purposes. Maximum **100 bytes**. Alphanumeric characters only.
</ParamField>

<ParamField body="campaign" type="string">
  Campaign name for grouping emails in analytics. Maximum **100 bytes**. Alphanumeric characters only.
</ParamField>

<ParamField body="trackOpen" type="integer">
  Set to `1` to enable open tracking for this email.
</ParamField>

<ParamField body="trackClick" type="integer">
  Set to `1` to enable link click tracking. To exclude a specific link from tracking, add the `ef:disable-tracking` attribute to its anchor tag.
</ParamField>

<ParamField body="uniqueMsgID" type="string">
  A unique message identifier for tracking and deduplication purposes. Maximum **50 bytes**.
</ParamField>

<ParamField body="attachment" type="object">
  A single file to attach to the email. Only one attachment is supported per request.

  <Expandable title="attachment fields">
    <ParamField body="attachment.fileName" type="string" required>
      The filename of the attachment, including its extension (e.g. `invoice.pdf`).
    </ParamField>

    <ParamField body="attachment.fileData" type="string" required>
      Base64-encoded content of the file to attach.
    </ParamField>
  </Expandable>
</ParamField>

<ParamField body="sandboxMode" type="boolean">
  Set to `true` to run a test send. The API validates and processes the request normally but does not deliver the email.
</ParamField>

***

## Response Fields

<ResponseField name="code" type="integer">
  `200` on success. See [Error Codes](#error-codes) for failure values.
</ResponseField>

<ResponseField name="message" type="string">
  Empty string (`""`) on success. Contains an error description on failure.
</ResponseField>

***

## Error Codes

| Code  | Cause                                                                                                                                                                                                                  |
| ----- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `400` | Missing required parameter; invalid `sendDate` format; `category`, `campaign`, or `uniqueMsgID` exceeds length limit; invalid recipient address; sender name too long; invalid reply-to address; missing email content |
| `403` | Sender address not registered; template not found; insufficient account credits                                                                                                                                        |

***

## Example

### Request

```bash theme={null}
curl --request POST \
  --url https://api.effilink.co/v5/transactional/mail/sends_customised \
  --header 'Content-Type: application/json' \
  --header 'ApiKey: YOUR_API_KEY' \
  --data '{
    "subject": "Your order has shipped",
    "content": "<p>Hello {{name}}, your order {{orderId}} has shipped!</p>",
    "params": {"name": "Jane", "orderId": "ORD-5678"},
    "senderMail": "noreply@yourdomain.com",
    "senderName": "Your Store",
    "to": {
      "email": "jane@example.com",
      "name": "Jane Smith"
    },
    "trackOpen": 1,
    "trackClick": 1,
    "category": "shipping",
    "campaign": "order_confirmation"
  }'
```

### Response

```json theme={null}
{
  "code": 200,
  "message": ""
}
```