DMARC
A policy that tells mailbox providers what to do when SPF or DKIM fail.
DMARC is a DNS TXT record that publishes a policy (none, quarantine, reject) and a reporting address. Google and Yahoos February 2024 bulk-sender requirements made DMARC mandatory at scale. Start with p=none, monitor reports for several weeks, then tighten.
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 dmarc, 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.