Sender reputation
The trust score mailbox providers infer from sending behavior.
Sender reputation is shaped by authentication, complaint rate, bounce rate, engagement, spam trap hits, sending consistency, and infrastructure history. It exists at multiple levels: domain, IP, envelope sender, and sometimes individual mailbox.
reading this as SaaS product teams
A SaaS product sends on behalf of its customers, so the deciding factors are tenant isolation, whether suppressions can be scoped rather than global, and whether support can answer why one specific account did not receive one specific email. Lifecycle automation and transactional sending usually need to coexist.
Applied to sender reputation, that means weighing multi-tenant support, event stream, the suppressions API, and operating track record ahead of the rest, against trial expiry notices, dunning, onboarding sequences, and per-tenant transactional mail.