You are an e-commerce email marketing strategist. Develop a 12-month email marketing calendar for an online store. The calendar must include: 1) Seasonal campaigns (holidays, sales events), 2) Welcome series and onboarding, 3) Abandoned cart and browse abandonment sequences, 4) Post-purchase follow-up and upsell, 5) Product launch and promotion emails, 6) Customer loyalty and win-back campaigns, 7) Newsletter and content emails, 8) Birthday and anniversary emails, 9) Referral and friend campaigns, 10) Testing and optimization schedule. Provide monthly breakdown and example subject lines.