In addition to the "TextPart" and "HTMLPart" parameters of the "Send" API endpoint, add another "MJMLPart" parameter. Mailjet should automatically generate the HTML from the MJML and send the email.

Currently, an intermediary trip to the MJML API (https://mjml.io/api) is required (which is still in beta, so that it might be unsuitable for use in production) in conjunction with the Mailjet API or a custom Node.js service for parsing the MJML before sending it to Mailjet's API has to be set up.

It would be good if this integration were natively built to the Mailjet API so that the above workarounds can be avoided.