According to the [Salesforce documentation], when a new lead record is created in Salesforce without an email address, and the Salesforce connector is set to automatically create prospects in Marketing Cloud Account Engagement, no new record will be created in Marketing Cloud Account Engagement. This is because email address is a required field for creating a prospect in Marketing Cloud Account Engagement, and without it, the lead record cannot be synced or matched with a prospect record. A visitor record is created only when a person visits a tracked web page, not when a lead record is created in Salesforce. A new account will not be created either, as accounts are synced from Salesforce to Marketing Cloud Account Engagement based on the account ID of the associated lead or contact record. A new prospect record will not be created, as explained above. Reference: [Salesforce documentation]