The overwhelming consensus among email experts, marketers, and documentation from major email service providers is that separating transactional and marketing emails is a critical best practice for maintaining optimal deliverability and protecting sender reputation. This separation can be achieved through dedicated IPs, subdomains, or separate sending domains, with authentication via SPF and DKIM being essential. Transactional emails generally have higher engagement and better deliverability, so isolating them from marketing emails, which can be more prone to deliverability issues, ensures that important transactional messages reach the inbox reliably. Proper IP warm-up is crucial when using dedicated IPs.