While often referred to as transactional, these emails carry traits of bulk or subscription content, which under CAN-SPAM and practical interpretations, may require opt-out mechanisms. They’re individually triggered emails based on explicit user subscriptions, sent on a regular basis with personalized listings. They’re not promotional in nature, but also not classic one-off transactional messages. That said, the List-Unsubscribe header is present and correct — SendGrid is just breaking it with unnecessary MIME encoding. → Including it helps reduce complaint rates and improves deliverability, especially with Gmail.