Starting October 31, 2026, you will need to submit a request to our support
　　desk to use the Email Sending API.

　　※Customers who are already using the service can continue to do so
　　without taking any action.

Provides an API that allows you to send bulk emails or single emails.

Provides a mechanism to send bulk mails by specifying a list of recipient addresses and the email body as parameters. You can also use the merge characters to create emails with different content for each destination address.

It also provides an API that allows you to easily send a single mail. You can send an email by using this API If external communication by SMTP is not possible due to restrictions of the ISP or cloud where the application is located.

Version

The format of POST parameters and response messages differs depending on the API version. Please refer to the API specifications of the version you use.

Current version is 2.

Common Specification

Common specification of the Transactional Email API will be explained in this section.

Access Point Host and URL

https://[hostname]/api/[version]/[resource]/[action].[format]

• [hostname] Represents the host name that provide this API.

• [version] represents the API version. You can specify v2.

• [resource] represents the resource of the operation.

• [action] represents the operation.

• [format] represents the format of the response message. You can specify json and xml.

　　Note

　　　The Email Sending API is provided by the mail server, similar to SMTP.

Specifies the access point host according to the service plan as follows.

sandbox

The free trial allows you to connect to the following endpoints:

transactional-email

Business / Enterprise / OEM / Pro plan allows you to connect to the following endpoints:

*) SUBDOMAIN Is the domain name you applied for when you start using the service.

Standard plan allows you to connect to the following endpoints:

Authentication

The Email Sending API performs a user authentication that uses the api_user and api_key parameters included in the HTTP request. For APU user registration please refer to "API user" in user guide.

HTTP Request

HTTP request specifications received by the Transactional Email API will be explained in this section.

Method

The Transactional Email API only accepts POST methods.

　　Note

　　　The maximum size of POST that the API accepts depends on the receive size
　　　in the relay server settings(mail). The body text is 3 bytes for Japanese In case
　　　of UTF-8 and 1 byte for ASCII.However,It is encoded in Base64 and becomes
　　　about 130%. Since the attachment file encoded in Base64,It will be about 130%
　　　of the original file size.

Header

Transactional Email API references the following header fields:

Content Type

Specifies application/x-www-form-urlencoded or application/json.

Specifies multipart/form-data since you need to upload the file If you want to send an email with an attachment.

Parameter

The Transactional Email API must include api_user, api_key, for user authentication in all HTTP requests and must send the parameters defined for each URL.

This document describes the parameters according to the following format.

• Parameter：The name of the parameter to POST.

• Required：If this parameter is required,Yes.

• Data Type：Data type of the parameter value.（Refer to below Data Type）

• Description：Description about this parameter.

For parameters with the restrictions such as default value and input value range, input in the following format in the description column.

• Default：(default value)

• Span：min=(minimum value) / max=(maximum value)

• Restrictions：Description about the restrictions on parameters. For example, 'start_date' must be equal to 'end_date' or a past date.

When specifying application/x-www-form-urlencoded (multipart/form-data)

Create the parameter name and the value set and then POST.

to use application/json

Create a JSON with the parameter name as property and POST it.

JSON

{
  "api_user" : "smtp_api_user@example.com",
  "api_key" : "a29yZWhhcGFzc3dvcmRkZXN1",
  "to" : [
    {
      "name" : "Personal Name1",
      "address" : "user1@example.com"
    },
    {
      "name" : "Personal Name2",
      "address" : "user2@example.com"
    }
  ],
  "from" : {
    "name" : "customer support",
    "address" : "support@example.co.jp"
  },
  "subject" : "~~~~shop：notification for member registration completion",
  "text" : "((#name#))  This time, ....."
}

Data Type

Transactional Email API handles data types according to the following specifications.

HTTP Response

HTTP response specifications received by the Transactional Email API will be explained in this section.

Status Code

The Transactional Email API responds with the following status code:

Header

The Transactional Email API responds to JSON or XML format messages according to the format specified in the URL.The format of these response messages is distinguish by the HTTP response header Content-Type.

Message

The Transactional Email API responds with the following message:

Successful

For the respond message when the request is successful, please refer to "Response" of each API specification.

Error

This message responds when the request fails.

JSON

{
    "errors" : [
        {
            "code" : "01-004",
            "field" : "api_user",
            "message" : "api_user is required."
        },
        {
            "code" : "01-004",
            "field" : "api_key",
            "message" : "api_key is required."
        }
    ]
}

XML

<errors>
    <error>
        <code>01-004</code>
        <field>api_user</field>
        <message>api_user is required.</message>
    </error>
    <error>
        <code>01-004</code>
        <field>api_key</field>
        <message>api_key is required.</message>
    </error>
</errors>

Error Message

Common error messages for the Transactional Email API is explained in the following. Apart from the common error message an error message defined for each API may be returned.

Security

Email sending API security will be explained in this section.

User Authentication

Email sending API performs a user authentication that uses the api_user and api_key parameters included in the HTTP request. For API user registration please refer to"API user" in user guide.

　　Note

　　　Since the Email Sending API authenticates the user by SMTP authentication,
　　　"SMTP" must be checked on.