How can separating mailstreams prevent cross-contamination?

Mailstream separation prevents 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.