email                 address|product code
garry123@gmail.com    |A123A
garry123@gmail.com    |AB263
ada121@hotmail.com    |45632A
ada121@hotmail.com    |78YU
garry123@gmail.com    |6543D

garry123@gmail.com|A123A,AB263,6543D
ada121@hotmail.com|45632A,78YU

SELECT
c.EmailAddress,
od.concat(productcode) as Product_SKU
FROM
OrderDetails od
JOIN Orders o
ON od.OrderID = o.OrderID
JOIN Customers c
ON c.CustomerID=o.CustomerID
WHERE
o.OrderDate BETWEEN 01/01/2016 AND getdate()
GROUP BY c.EmailAddress