With the transactional email add-on, you can use the single-send API to merge custom properties. Use this endpoint to render the email, add some customizations, and send the email to the intended recipient.
- In your HubSpot account, navigate to Marketing > Email.
- Create a new email.
- In the main email body, insert the desired personalization tokens. To use a custom property that doesn't exist yet, click the source code icon code and add the token in the code of your email.
- Click the Settings tab and use the Email type dropdown menu to select Transactional.
- Click the Recipients tab and select Save for single-send API.
- Click the Review tab, then click Save for single-send API.
- In the dialog box, click Save email for single-send API. Once saved, you'll get an internal email ID to use with the API in the email Performance tab.
- Copy the internal email ID, then click Go to documentation to push values to the personalization tokens in your email.
Please note: you can find the internal email ID at any time in the email details. In your HubSpot account, navigate to Marketing > Email. Click the name of the email, then click More details to see the Internal email ID in the slide-in panel.