Duplicates in Marketo

Well, Marketo identifies people by Lead ID, not by email address. So technically, you can have multiple records with the same email address, even if other fields (like Title) are different. However, there are a few implications to be aware of:

1. When sending emails, Marketo automatically deduplicates by email address at send time.
   So if two records share the same email address, only one email will be sent.
2. If you are syncing with Salesforce, duplicates can cause issues depending on how your SFDC duplicate rules are configured.

3. When an email address is included in a list import, it attaches to the most recently updated record in Marketo.

4. Check this Community post for more deets: 

It’s generally recommended to deduplicate records and maintain one record per email address whenever possible. Is there any specific business case for which you need more than 1 record with the same email address in your system?

Piggybacking on Darshil’s response, how are you getting these duplicates? Ideally, you need to stop duplicate creation at the source, as merging afterward is difficult-to-impossible.