To reduce spam complaints in transactional emails, it's essential to put yourself in the shoes of the message recipient and provide value to them. Setting frequency expectations and allowing recipients to control how often they receive messages can help prevent unwanted messages and spam complaints. Making it clear who is sending the email and why, using accurate and descriptive subject and metadata, and ensuring that the content matches the expectation set by the subject line are also crucial. Following best practices for email design and content, testing messages for spam and design problems, protecting forms against spambot abuse, and monitoring spam complaints across your entire domain can also help reduce spam complaints. By implementing these strategies, businesses can improve their deliverability, provide a clear and happy experience for their customers, and avoid getting marked as spam.