Step 1. Create a segment of customers who bough a specific product on your store.
Customers tab > Manage Segments > Create Segment > Choose "Have performed event", "Order Success" >> tick With data >> event Product >> Add Product "Jeans" to the list box
Key: Product ID can be found as following
You can also add the product ID to the list box instead �of searching every single product from the box
Step 2. Apply this segment to suitable newsletter/ campaign