Keep Subject Line Concise: Use 50-60 characters; include key words like "Payment Received" Personalize With Name: Use {customer_name} placeholder to address customer directly Include Receipt Details: Always show {amount_paid}, {invoice_number}, and {transaction_id} Provide Link to Invoice: Include {invoice_link} for easy reference Express Gratitude: Thank customers for their payment and business Clear Structure: Use formatting and line breaks to make email scannable Professional Tone: Match your brand voice - appreciative and professional Test Before Deploying: Send test emails to verify all placeholders work Mobile Friendly: Keep email width standard (around 600px) Include Contact Info: Provide customer support contact for questions