Send Transactional Email: Customer.io action

Inputs

The fields this action accepts.

Every field can be mapped from an upstream trigger, AI step, table row, or hard-coded literal.

Field	Type	Required	Description
Transactional Message ID transactional_message_id	string	Required	The ID of the transactional message template in Customer.io
To Email to	string	Required	To Email. e.g. "user@example.com"
Customer Email (identifier) identifiers_email	string	Required	Customer Email (identifier). e.g. "user@example.com"
Template Data (JSON) message_data	string	Optional	Variables to populate the template
Subject Override subject	string	Optional	Override the template subject

Sample request

{
  "transactional_message_id": "e.g. 1",
  "to": "user@example.com",
  "identifiers_email": "user@example.com",
  "message_data": "{\"name\": \"John\", \"order_id\": \"12345\"}",
  "subject": "e.g. Your order #12345 is confirmed"
}

Returns

{
  "queued_at": 1700000000,
  "delivery_id": "abc-123"
}

Use these fields in downstream nodes for routing, logging, or error handling.

FAQ

Questions about Send Transactional Email.

What does the Send Transactional Email action do in Customer.io?

Fires a transactional template (designed in Customer.io UI) at a specific recipient with merge data. For "password reset, order confirmation, receipt" workflows where the email content is reviewed in CIO but the trigger is external.

What inputs does Send Transactional Email require?

Required: Transactional Message ID, To Email, Customer Email (identifier). Every input accepts a static value or a variable from any upstream node in your workflow.

Can I use dynamic inputs from earlier workflow nodes?

Yes. Any field on this action can pull values from upstream nodes, whether that's a form response, a trigger payload, an AI output, or a lookup result.

What happens if Customer.io returns an error?

The workflow pauses on the failed node, the error message is captured in the run log, and you can retry the run with one click. Auto-retry policies are configurable per workflow with exponential backoff up to 5 attempts.

Does Send Transactional Email support batch operations?

Yes. Run Send Transactional Email inside a Loop node to process arrays. Tiny Command handles Customer.io's rate limits automatically so you don't have to throttle manually.

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