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Use single-send in an email to merge custom properties

Last updated: January 11, 2021

Applies to:

All products and plans

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.

Please note: HubSpot will deliver a transactional email to a contact regardless of their subscription status or their double opt-in status.

  • 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.


If you need to locate the internal email ID at a later point, you can find it in the email details panel:

  • In your HubSpot account, navigate to Marketing > Email.
  • Click the name of the email.
  • Click More details to see the Internal email ID in the right panel.