How can separating mailstreams prevent cross-contamination?

Risk scenario without separation:

• Marketing campaign gets complaints
• Reputation drops for shared domain
• Transactional delivery suffers
• Password resets not delivered

With separation:

• Marketing issues affect marketing.domain only
• Transactional.domain reputation remains intact
• Critical emails still delivered

Separation strategies:

• Different subdomains per stream
• Different IPs per stream
• Different ESPs for critical vs bulk

Trade-offs:

• More complex setup
• More authentication records to manage
• But much better risk management
• Contaminated cargo in one ship does not spoil cargo in another ship.