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 developers picking email infrastructure
The question here is which one a backend engineer would rather operate. That means SDK depth in the language already in use, whether a retry can safely be replayed, how much the event log tells you when a customer says the email never arrived, and whether the pricing curve stays sane as volume grows.
Applied to ip warming, that means weighing developer experience, SDK breadth, idempotency keys, and operating track record ahead of the rest, against password resets, receipts, and magic links shipped from application code.