Hi @PAllmond,
HubSpot automatically deduplicates contacts by email address. No two contacts can exist with the same email address, it’s the unique identifier in HubSpot. The same goes for companies with company domains. These automations are explained here: Deduplicate records in HubSpot (Records without email address or company domain name will be created as separate records in HubSpot, causing duplicates.)
If you want to deduplicate by other fields, you could either use the deduplication tool in HubSpot (which suggests duplicates for manual deduplication) or a third-party solution like Insycle.
Best regards!