Salesforce ' s documented deliverability guidance recommends separating transactional and commercial email traffic onto distinct Sender Authentication Packages (and correspondingly, distinct sending domains/IP reputations where applicable) because the two traffic types have fundamentally different engagement and complaint profiles — transactional messages (password resets, receipts) typically have very high open rates and near-zero complaints, while commercial/marketing messages carry more variable engagement and higher complaint risk. Mixing both traffic types under a single SAP/domain risks commercial-send reputation issues bleeding over and degrading deliverability for critical transactional messages, so maintaining separate SAPs isolates and protects each traffic type ' s sender reputation independently. Option A ' s specific 500,000-message shared-IP threshold is not accurate guidance tied to this scenario ' s core concern. Option C ' s blanket ' one dedicated IP per 100,000 messages ' ratio is an oversimplified and inaccurate rule; dedicated IP warm-up and volume thresholds depend on multiple deliverability factors beyond a fixed per-100,000 ratio. Option D ' s claim that a minimum monthly volume is required ' to maintain sender reputation ' inverts the actual guidance, which is generally about maintaining consistent (not necessarily minimum) sending volume and quality to build and preserve reputation over time. Reference: Sender Authentication Package Best Practices, Transactional vs. Commercial Sending.