IP warming
Gradually ramping volume on a new IP to build reputation.
Mailbox providers (Gmail, Outlook, Yahoo) treat brand-new IPs with suspicion. Warming means sending small volumes for the first weeks, ramping up gradually, and prioritizing engaged recipients. Required for dedicated IPs and self-hosted setups.
reading this as teams choosing a transactional API
Judged purely as an API. What the request contract guarantees on retry, how complete the webhook event coverage is, whether suppressions are readable and writable programmatically, and how much the message log retains when something needs debugging in production.
Applied to ip warming, that means weighing idempotency keys, webhook coverage, event stream, and operating track record ahead of the rest, against high-frequency programmatic sends where a missed delivery is a product failure.