Report to show only Tickets from Contacts w/ Multiple Open Tickets

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I am rather new to building custom reports, so please bear with me if I am not using correct terminology.

I'm attempting to make a report that only shows tickets of customers who have more than one open ticket (Unresolved, Updated, *NOT Solved*, etc). 

My organization's agents consolidate information from multiple tickets onto one thread and then close the duplicates - having a report that displays only the incidents that are from customers with multiple open tickets would help our agents consolidate the data more quickly. Currently to do this, an agent must sort the queues by email and look for multiple lines of the same address.