Skip to main content
Need to send attachments with your transactional email? Just reach out to us and we can enable the feature on your account.

​
Sending attachments

Check out the transactional API documentation for a refresher on the transactional API email payload. To attach a file to a transactional message, you’ll need to add a attachments key to the standard transaction API email payload. The attachments key should be an array of objects, each with the following keys:
  • filename - the name of the file
  • contentType - the MIME type of the file
  • data - the base64 encoded content of the file
Here’s an example of a transactional email payload with this ICS file attached: 
{
  "transactionalId": "*********",
  "email": "phil+attachments@loops.so",
  "attachments": [
    {
      "filename": "oil-change-invite.ics",
      "contentType": "text/calendar",
      "data": "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"
    }
  ]
}
When you send this payload, the recipient will receive an email with the ICS file attached: An email with an ICS file attached
All the usual transactional API email payload keys are still required. The attachments key is in addition to the standard payload.

​
Limitations

  • The total size of the JSON request body must be less than 4 MB. Keep in mind that attachments are base64 encoded, which increases file size by ~33%.
  • Attachments are not generally available. Please contact us if you need this feature enabled on your account.
Last modified on December 10, 2025