Email to Case (Automatic Record Creation) when sender is duplicated in CRM (both with same email addresses)

Hi, 

Does anyone know how CRM handles incoming emails and automatic record creation when there are duplicate contacts in CRM with the same email address?

For example, if you have an Automatic Case Creation rule on incoming emails, how does CRM determine which contact to associate the Case with? Will CRM always link new cases to the same Contact?

PS - I know that there should be detection rules in place to stop the duplicate Contacts from being created in the first place, but would like to know how CRM handles this situation in the event that some duplicates are missed. 

Thanks!