Find the emails of customers who has filed a complaints of the product with the most complaints.
SELECT t1.email_address FROM customers AS t1 JOIN complaints AS t2 ON t1.customer_id  =  t2.customer_id GROUP BY t1.customer_id ORDER BY count(*) LIMIT 1
SELECT t1.email_address FROM customers AS t1 JOIN complaints AS t2 ON t1.customer_id  =  t2.customer_id GROUP BY t1.customer_id ORDER BY count(*) LIMIT 1
[{'email_address': 'hsteuber@example.org'}]