Hi @Michele,
Thank you for your feedback! In HubSpot, we deduplicate contacts using email and usertoken as the 2 unique identifiers. At this time, we are not planning to add the functionality of having duplicates with the same email to our CRM. Using email and usertoken has proven effective to reduce duplicate records and maintaining data quality. This behavior is also fundamental to the functionality of other tools including imports, email sends and form submissions.
For more information on how the integration handles duplicates in Salesforce check out our knowledge documentation here.
If we decide to revisit this functionality at a later date, we will update this idea.
Please let me know if you have any further questions,
Cara