The hard part of a healthtech signup email isn't calling a send API. It's proving that a dedicated domain is ready for more welcome-email traffic without losing the evidence needed to explain each verification link later.
Short answer: use a gradual warmup plan controlled by four signals — authenticated identity, recipient legitimacy, delivery outcomes, and verification outcomes — and raise sending volume only after the current cohort produces complete evidence. A calendar can set the earliest promotion time; it shouldn't promote the domain by itself.
This changes the usual ramp. Instead of promising a universal 7-day or 30-day schedule, define stages as ceilings, admit only expected signup traffic, and hold or step back whenever the evidence is incomplete. The sending service can be Node.js, Python, or another stack because the decision belongs at the queue boundary, before any provider-specific adapter.
Keep it boring.
What should a Node.js transactional email warmup API monitor before raising sending volume?
