We’re sending transactional emails through the HubSpot Single Send API. According to your documentation:
Any emails sent through this API will automatically be associated with contact records based on the email address. If there is no contact with a matching email address, a new contact with that email will be created
However, we’re finding that new contacts are not being created from the email addresses we’re successfully sending to. We can see the recipients listed against an email within HubSpot, but not in the list of contacts, and clicking on their email address results in a 404.
How can we ensure contacts get created as a result of sending through this API?