Domain warming
Gradually ramping volume on a new sending domain so ISPs can build positive reputation before high-volume sends.
Domain warming is the process of gradually ramping email volume on a new sending domain (or a domain that hasn't sent in a long time) so that mailbox providers build positive reputation before you attempt high-volume sends. Cold-sending 100,000 emails from a fresh domain almost guarantees a deliverability disaster — most will land in spam or be outright rejected.
A standard warming schedule starts at 50–100 emails per day, doubles roughly every 2–3 days, and reaches full volume after 3–6 weeks. Sends during warming should go to your most engaged segment (recent signups, recent openers) so the engagement signals are strong. Sends to dormant segments during warming will tank your nascent reputation.
Warming applies to both your sending domain (the From: domain) and any subdomains used for specific email programs. Many senders split transactional sends and marketing sends onto separate subdomains so a marketing-side reputation problem doesn't poison transactional delivery.