Short answer: for a small SaaS sending fintech password-reset email, start with a standards-based sending setup and a local suppression gate; use a polling API only when the delay between a bounce or complaint and the next decision fits the SLO. A short token expiry does not compensate for sending to a recipient who should already be suppressed.
That is the decision rule I would take into a platform review. The integration should be boring: the application submits a message, records an operation ID, reads delivery events on a schedule, and changes its local send decision only after a durable write. Warmup is a traffic policy around that loop, not a switch that repairs sender reputation.
The password-reset case makes the distinction visible. A reset link may expire in ten minutes, but an email event can arrive later than that. The user-facing security guarantee and the delivery-control guarantee are separate systems.
What does a small SaaS need before it calls a password-reset email reliable?
First, define the message contract. A reset request should create a short-lived, single-use token, avoid placing sensitive account data in the message, and expose a neutral response so an attacker cannot use the endpoint to enumerate accounts. The mail worker should receive a message ID and a recipient decision, not decide eligibility from an old dashboard export.
