There's a new version of the HubSpot API

As of November 30, 2022, HubSpot API keys are no longer a supported authentication method for accessing HubSpot APIs. Instead, you should use a private app access token or OAuth to authenticate API calls. Learn more about this change and how to migrate an API key integration to use a private app instead.

How Does HubSpot validate email addresses?

HubSpot will validate the email address used for any process that would create or update a contact record.  This includes using the Contacts API to create or update a contact directly, and also the processing of any form submissions or events. Learn more about how HubSpot validates email addresses.