A person record in Marketo is getting created by the CRM sync even though there is a previously existing record existing in the Marketo database with the same email address.
By design, Marketo does not run the standard de-duplication process on records that come from your CRM. If you wish to prevent duplicates from coming over from your CRM, you would need to hide them from the Marketo sync user on the CRM side, or work with Marketo support to set up a custom sync filter.
Who This Solution Applies To
All Marketo instances with a native CRM integration