Shared IP
A sending IP used by many customers of a provider.
Most senders start on a shared IP pool. Reputation is collective: one bad sender can drag the pool down, but established providers actively manage their pools. Below 100k/month, shared IPs are usually preferable to dedicated.
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 shared ip, 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.