Send Email API

The transmission API lets you to send emails to numerous recipients.

Note: Transmission refers to a campaign. For example, transmission_id means the campaign's unique ID.

Request Type

POST

Request URL

https://campaigns.zoho.com/emailapi/v2/transmission

Content-Type

application/json

List of Request Body Attributes

Parameters	Data Type	Description
transmission_name	String	A user-defined identifier for the transmission (Max length: 150).
recipients	JSON array	An array of recipient objects containing information about who will receive the message. Each object may include merge data and additional metadata.
recipients[].address	String	Email address of the recipient (Max length: 100).
recipients[].name	String	Optional display name associated with the recipient’s address. (Max. length: 100).
recipients[].additional_data	JSON Object	Optional JSON object containing arbitrary user-defined metadata about the recipient (e.g., phone number, country, or internal identifiers).
recipients[].merge_data	JSON Object	A JSON object containing key-value pairs used for merge tag substitution in the email subject or content. Keys correspond to merge tags defined in the message, and values replace those tags during rendering. Example: $[first_name\|Customer]$ substitutes first_name or the default value Customer.
recipient_list_id	String	ID referencing a pre-saved recipient list. When provided, the system loads recipients from the associated list instead of requiring an explicit recipients array in the request payload.
options	JSON Object	Optional configuration settings that control email processing and delivery behaviour.
options.open_tracking	String	Enables or disables open-tracking for the transmission. Values: enabled/disabled Default: enabled
options.click_tracking	String	Enables or disables click-tracking for the transmission. Values: enabled/disabled Default: enabled
options.schedule_at	Long	Timestamp (in milliseconds) representing when the message should be scheduled for delivery. If omitted, the message is delivered immediately.
content	JSON Object	Defines the email content, sender identity, and related rendering rules.
content.from	JSON Object	Specifies the sender of the email.
content.from.address	String	Required email address of the sender (Max length: 100).
content.from.name	String	Optional display name of the sender (Max length: 100).
content.reply_to	String	Optional reply-to address. Replies to the email will be directed to this address instead of the sender (Max length: 100).
content.subject	String	Email subject line. Supports merge tags for personalisation. (Max length: 200).
content.html	String	HTML version of the email body. Merge tags within the content are replaced using merge_data.
content.text	String	Plain-text version of the email body. Merge tags are also supported in this field. If content.html node is provided, text need not be specified as it is automatically generated.
content.attachments	JSON Array	List of files to be sent as email attachments. Each attachment must include a file name and Base64-encoded file data.
content.attachments[].name	String	File name of the attachment, including extension. e.g., report.pdf (Max length: 100)
content.attachments[].data	String	Base64-encoded content of the file.
content.template_id	String	ID referencing a pre-saved email template. When provided, the system loads HTML and/or text content from the stored template instead of requiring content.html and content.text fields in the payload.

List of Response Body Attributes

Parameters	Data Type	Description
rejected_recipients	Integer	The count of the recipients rejected by our API. Rejection maybe due to invalid syntax.
accepted_recipients	Integer	The count of the recipients accepted by our API.
response	JSON Object	Contains the response details of the API.
code	Integer	Success or failure code.
message	String	Success or failure message returned by the API.
transmission_id	String	Unique ID of the transmission.
errors	JSON Array	Contains the error details of the API such as 'code' and 'message'.

Unsubscribe Link

Unsubscribe links can be included in the content using an anchor tag with the attribute data-zcea-unsubcribe="1". Refer to the 'Sample Request Payload for transmission with unsubscribe link' to your right. If you had configured an unsubscribe webhook, it will be called when a contact clicks this link. This webhook will contain the contact details, from which you can get the contact email and add them to your suppression list using our Suppression API.

Attachments

Attachments are supported only for transmissions that include more than one recipient.
Attachments must be Base64-encoded.
File names must include an extension.
Maximum total attachment size per transmission: 5 MB.
Maximum no. of attachments: 5
Attachments are validated for file type and size. Unsupported or restricted file types may be rejected for security reasons.

Possible Error Cases

Error Codes	Description
400001	Transmission name not provided.
400002	The recipient list is not provided.
400003	Content details are not provided.
400004	Sender details are not provided.
400005	The sender address is not provided.
400006	Subject is not provided.
400007	Content body is not provided.
400008	Invalid sender address.
400009	The sender domain is not authenticated. Please authenticate your domain before sending emails.
400011	Recipient limit exceeded.
400012	CNAME record not verified for bounce domain.
400013	None of the recipients are valid.
400015	Your account license has expired.
400016	You do not have sufficient credits to perform this action.
400017	Schedule time is lesser than current time.
400024	Invalid tracking option.
400025	Invalid Reply-To address.
400026	Your trial period has ended.
400027	The transmission name exceeds the maximum allowed length.
400028	The subject exceeds the maximum allowed length.
400029	The from address exceeds the maximum allowed length.
400030	The from name exceeds the maximum allowed length.
400031	The reply-to address exceeds the maximum allowed length.
400032	The content exceeds the maximum allowed length.
400033	No attachments provided.
400034	One or more attachments missing name.
400035	One or more attachments have invalid name.
400036	Name too long for one or more attachments.
400037	One or more attachments missing data.
400038	One or more attachments missing file extension.
400039	One or more attachments have invalid type.
400040	Attachments limit exceeded. You cannot add more than 5 attachments.
400041	Total attachments size exceeds the allowed limit. You cannot add more than 5 MB.
400042	Attachments are not supported for Single Recipient Transmissions.
400043	The name of one or more recipients exceeds the maximum allowed length.

Run in Postman View Collection

Sample Request Payload for Transmission with inline content

Copied{
 "transmission_name": "hello_customer",
 "recipients": [
   {
     "address": "lucy@example.campaigns.zoho.com",
      "name": "Lucy Girea",
      "additional_data": {
        "phone" : "+919876543210",
        "country": "CA"
     },
     "merge_data": {
       "first_name": "Lucy"
     }
   }
 ],
 "content": {
   "from": {
     "address": "aron@marketing.campaigns.zoho.com",
     "name": "Aron Fletcher"
   },
   "subject": "Hello $[first_name|Customer]$, Welcome to Zylker",
   "html": "<html><body>Welcome $[first_name|Customer]$, your content here!<br></body></html>",
 }
}

Sample Request Payload for Transmission with pre-configured recipient list

Copied{
  "transmission_name": "hello_customer",
  "recipient_list_id": "8000000097065",
  "content": {
    "from": {
      "address": "aron@vnaash.in",
      "name": "Aron Fletcher"
    },
    "subject": "Welcome to Zylker 2",
    "text": "Welcome, $[first_name]$, your content here!"
  }
}

Sample Request Payload for Transmission with template content

Copied{
  "transmission_name": "hello_customer",
  "recipients": [
    {
      "address": "lucy@example.campaigns.zoho.com",
      "additional_data": {
        "phone": "+919876543210",
        "country": "CA"
      },
      "merge_data": {
        "first_name": "Lucy"
      }
    }
  ],
  "content": {
    "from": {
      "address": "aron@vnaash.in",
      "name": "Aron Fletcher"
    },
    "subject": "Welcome to Zylker 2",
    "template_id": "8000000124003"
  }
}

Sample Request Payload for scheduled transmission

Copied{
  "transmission_name": "hello_customer",
  "recipients": [
    {
      "address": "lucy@example.campaigns.zoho.com",
      "name": "Lucy Girea",
      "additional_data": {
        "phone": "+919876543210",
        "country": "CA"
      },
      "merge_data": {
        "first_name": "Lucy"
      }
    }
  ],
  "options": {
    "schedule_at": 1728366058000
  },
  "content": {
    "from": {
      "address": "aron@marketing.campaigns.zoho.com",
      "name": "Aron Fletcher"
    },
    "subject": "Welcome to Zylker",
    "html": "<html><body>Welcome $[first_name|Customer]$, your content here!<br></body></html>"
  }
}

Sample Request Payload for transmission with tracking disabled

Copied{
  "transmission_name": "hello_customer",
  "recipients": [
    {
      "address": "lucy@example.campaigns.zoho.com",
      "name": "Lucy Girea",
      "additional_data": {
        "phone": "+919876543210",
        "country": "CA"
      },
      "merge_data": {
        "first_name": "Lucy"
      }
    }
  ],
  "options": {
    "open_tracking": "disabled",
    "click_tracking": "disabled"
  },
  "content": {
    "from": {
      "address": "aron@marketing.campaigns.zoho.com",
      "name": "Aron Fletcher"
    },
    "subject": "Welcome to Zylker",
    "html": "<html><body>Welcome $[first_name|Customer]$, your content here!<br></body></html>"
  }
}

Sample Request Payload for transmission with unsubscribe link

Copied{
  "transmission_name": "hello_customer",
  "recipients": [
    {
      "address": "lucy@example.campaigns.zoho.com",
      "additional_data": {
        "phone": "+919876543210",
        "country": "CA"
      },
      "merge_data": {
        "first_name": "Lucy"
      }
    }
  ],
  "content": {
    "from": {
      "address": "aron@vnaash.in",
      "name": "Aron Fletcher"
    },
    "subject": "Welcome to Zylker 2",
    "html": "<html><body>Welcome $[first_name|Customer]$, your content goes here <br/><br/> <a href=\"https://zylker.com.com/unsubscribe\" data-zcea-unsubscribe=\"1\" title=\"Unsub\">Unsubscribe</a></body></html>"
  }
}

Sample Request Payload for transmission with reply-to address

Copied{
  "transmission_name": "hello_customer",
  "recipients": [
    {
      "address": "lucy@example.campaigns.zoho.com",
      "name": "Lucy Girea",
      "additional_data": {
        "phone": "+919876543210",
        "country": "CA"
      },
      "merge_data": {
        "first_name": "Lucy"
      }
    }
  ],
  "content": {
    "from": {
      "address": "aron@marketing.campaigns.zoho.com",
      "name": "Aron Fletcher"
    },
    "reply_to": "aron@reply.campaigns.zoho.com",
    "subject": "Welcome to Zylker",
    "html": "<html><body>Welcome $[first_name|Customer]$, your content here!<br></body></html>"
  }

Sample Request Payload for transmission with attachments

Copied{
  "transmission_name": "hello_customer",
  "recipients": [
    {
      "address": "lucy@example.campaigns.zoho.com",
      "name": "Lucy Girea",
      "additional_data": {
        "phone": "+919876543210",
        "country": "CA"
      },
      "merge_data": {
        "first_name": "Lucy"
      }
    },
    {
      "address": "andrew@example.campaigns.zoho.com",
      "name": "Andrew Smith",
      "additional_data": {
        "phone": "+11234567890",
        "country": "US"
      },
      "merge_data": {
        "first_name": "Andrew"
      }
    }
  ],
  "content": {
    "from": {
      "address": "aron@marketing.campaigns.zoho.com",
      "name": "Aron Fletcher"
    },
    "reply_to": "aron@reply.campaigns.zoho.com",
    "subject": "Welcome to Zylker",
    "html": "<html><body>Welcome $[first_name|Customer]$, your content here!<br></body></html>",
    "attachments": [
      {
        "name": "invoice.pdf",
        "data": "JVBERi0xLjQKJc..."
      },
      {
        "name": "notes.txt",
        "data": "SGVsbG8gd29ybGQ="
      }
    ]
  }

Sample Response - Success

Copied{
   "rejected_recipients": 1,
   "accepted_recipients": 1,
   "response": {
       "code": 200001,
       "message": "Your transmission has been scheduled successfully"
   },
   "transmission_id": "146429000000058021"
}

Sample Response - Failure

Copied{
   "errors": [
       {
           "code": 400012,
           "message": "CNAME not verified for bounce domain"
       },
       {
           "code": 400009,
           "message": "Sender domain not authenticated. Please authenticate your domain before sending"
       }
   ]
}