API Reference¶

The InteSys Transactional Email API (powered by FrontEngine) is an HTTP JSON-based API with RPC-style endpoints. Each action has its own endpoint. All requests use HTTPS with POST method and JSON-encoded parameters.

Base URL: https://app1.frontengine.net

Authentication¶

All API requests require the X-Server-API-Key header with your server API key.

X-Server-API-Key: your-api-key-here

Obtain your API key from the InteSys client portal or contact support.

Keep Your API Key Secret

Never expose your API key in client-side code, public repositories, or logs. Rotate keys immediately if compromised.

Authentication Errors¶

Error	Description
`InvalidServerAPIKey`	The provided token is invalid. Response includes the rejected `token` value.
`ServerSuspended`	The mail server associated with your credentials has been suspended.

Response Format¶

All API responses follow this structure:

{
  "status": "success",
  "time": 0.23,
  "flags": {},
  "data": {}
}

Field	Type	Description
`status`	string	`success`, `parameter-error`, or `error`
`time`	float	Server-side processing time in seconds
`flags`	object	Additional metadata (pagination, etc.)
`data`	object	Response payload or error details

HTTP Status Codes¶

Code	Meaning
`200`	Request processed (check `status` field for result)
`301` / `308`	Redirect (usually http to https)
`500`	Unexpected server error
`503`	Service unavailable (maintenance)

Send API¶

Send Message¶

Send a transactional email with full control over headers, body, and attachments.

POST /api/v1/send/message

Parameters:

Parameter	Type	Required	Description
`to`	array	Yes	Recipient email addresses (max 50)
`cc`	array	No	Carbon copy addresses (max 50)
`bcc`	array	No	Blind carbon copy addresses (max 50)
`from`	string	Yes	Sender email address (must be verified domain)
`sender`	string	No	Sender header (if different from `from`)
`subject`	string	Yes	Email subject line
`tag`	string	No	Classification tag for filtering in analytics
`reply_to`	string	No	Reply-to address
`plain_body`	string	No*	Plain text email content
`html_body`	string	No*	HTML-formatted email content
`attachments`	array	No	File attachments (see below)
`headers`	object	No	Custom email headers
`bounce`	boolean	No	Whether this message is a bounce response

*At least one of html_body or plain_body must be provided.

Attachment Object:

Field	Type	Description
`name`	string	Filename (e.g., `invoice.pdf`)
`content_type`	string	MIME type (e.g., `application/pdf`)
`data`	string	Base64-encoded file content

Error Codes:

Error	Description
`ValidationError`	General parameter validation failure
`NoRecipients`	No recipient addresses provided
`NoContent`	Neither `html_body` nor `plain_body` provided
`TooManyToAddresses`	More than 50 `to` addresses
`TooManyCCAddresses`	More than 50 `cc` addresses
`TooManyBCCAddresses`	More than 50 `bcc` addresses
`FromAddressMissing`	No `from` address specified
`UnauthenticatedFromAddress`	Sending domain not verified for this server
`AttachmentMissingName`	Attachment provided without filename
`AttachmentMissingData`	Attachment provided without data

Example: curl¶

curl -X POST https://app1.frontengine.net/api/v1/send/message \
  -H "X-Server-API-Key: your-api-key" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "[email protected]",
    "to": ["[email protected]"],
    "subject": "Order Confirmation #12345",
    "html_body": "<h1>Thank you for your order!</h1><p>Order #12345 has been confirmed.</p>",
    "plain_body": "Thank you for your order! Order #12345 has been confirmed.",
    "tag": "order-confirmation",
    "reply_to": "[email protected]"
  }'

Example: Python¶

import requests

response = requests.post(
    "https://app1.frontengine.net/api/v1/send/message",
    headers={
        "X-Server-API-Key": "your-api-key",
        "Content-Type": "application/json",
    },
    json={
        "from": "[email protected]",
        "to": ["[email protected]"],
        "subject": "Welcome!",
        "html_body": "<h1>Welcome to our platform!</h1>",
    },
)

print(response.json())

Example: Node.js¶

const response = await fetch(
  "https://app1.frontengine.net/api/v1/send/message",
  {
    method: "POST",
    headers: {
      "X-Server-API-Key": "your-api-key",
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      from: "[email protected]",
      to: ["[email protected]"],
      subject: "Welcome!",
      html_body: "<h1>Welcome to our platform!</h1>",
    }),
  }
);

const data = await response.json();
console.log(data);

Send Raw (RFC2822)¶

Send a pre-formatted RFC2822 message. Useful for applications that construct their own MIME messages.

POST /api/v1/send/raw

Parameters:

Parameter	Type	Required	Description
`mail_from`	string	Yes	Envelope sender address
`rcpt_to`	array	Yes	Recipient addresses for delivery
`data`	string	Yes	Base64-encoded RFC2822 message
`bounce`	boolean	No	Whether this is a bounce response

Error Codes:

Error	Description
`UnauthenticatedFromAddress`	Sender domain not verified for this server

Messages API¶

Get Message Details¶

Retrieve complete details about a sent message.

POST /api/v1/messages/message

Parameters:

Parameter	Type	Required	Description
`id`	integer	Yes	The message ID
`_expansions`	array/boolean	No	Request additional data fields. Pass `true` for all expansions or an array of expansion names.

Error Codes:

Error	Description
`MessageNotFound`	No message found with the provided ID

Get Delivery Attempts¶

Retrieve all delivery attempts for a specific message.

POST /api/v1/messages/deliveries

Parameters:

Parameter	Type	Required	Description
`id`	integer	Yes	The message ID

Error Codes:

Error	Description
`MessageNotFound`	No message found with the provided ID

Next Steps¶

Authentication — Configure SPF, DKIM, and DMARC for your sending domain
Webhooks — Receive real-time delivery event notifications