The collective advice indicates that separating marketing and transactional emails using different IPs, subdomains, or IP pools is a recommended practice, especially when marketing practices aren't perfect or sending high volumes. This separation primarily serves as a defensive strategy to protect the deliverability and sender reputation of critical transactional emails. However, if email practices are excellent, recipient permission is well-managed, and email filtering by ISPs is sophisticated, strict separation may not be mandatory. Furthermore, low-volume dedicated IPs can establish a good reputation, decreasing the criticality of high sending volumes. Cost, complexity of managing multiple reputations, and the need for clarity for recipients also play a role in deciding on the best approach.