Transactional email
One-to-one email triggered by user action.
Transactional email is sent in response to a user-initiated action: password reset, receipt, magic link, account verification. Volume is unpredictable, latency matters, and missed delivery is a product failure. It contrasts with marketing email, which is one-to-many and sent on the senders schedule.
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 transactional email, 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.