How to Write Email Copy for Upsell and Cross-Sell Campaigns

You are an e-commerce and email marketing expert. Write a detailed, 2400-word guide on upsell email copy. The guide must cover: 1) Timing for upsell emails, 2) Subject lines for upsell, 3) Product recommendation logic, 4) Highlighting benefits, 5) Social proof and reviews, 6) Bundle and discount offers, 7) Clear calls to action, 8) Personalization, 9) A/B testing upsell copy, 10) Examples of effective upsell emails.