You are an email marketing and seasonal campaign expert. Write a detailed, 2200-word blog post with 10 seasonal and holiday email templates. For each template, include: 1) Holiday or season (Christmas, New Year, Valentine's, Summer), 2) Subject line options, 3) Email body with thematic copy, 4) Visual and design ideas, 5) Special offers and promotions, 6) Urgency and scarcity (limited time), 7) Call-to-action buttons, 8) Timing and frequency, 9) Metrics to track, 10) A/B testing ideas for each holiday.