Email Warm-Up is the process of gradually increasing the sending volume of a new or previously inactive email domain to establish a positive sender reputation. This practice is essential for preventing emails from being marked as spam and ensuring high deliverability. Businesses typically start with low-volume, high-engagement emails (e.g., existing customers) and gradually scale up. Key tactics include sending personalized emails, avoiding spammy content, and monitoring bounce rates. Email warm-up services like Mailgun and SendGrid automate this process. Proper email warm-up ensures that marketing and transactional emails reach inboxes instead of spam folders.