IP warmup is the practice of gradually increasing send volume on a new IP so mailbox providers build a reputation profile without triggering anti-spam heuristics.
The schedule. Day 1, 50 sends. Day 2, 100. Double daily through day 7. Then increase 50% daily until target volume. Most warmups take 14-30 days.
The audience matters more than the schedule. Start with your most-engaged subscribers — recent signups, frequent openers, recent clickers. Their positive engagement signals tell mailbox providers your IP is legitimate. Save unengaged segments for the end of warmup.
Monitor postmaster scores daily. Gmail Postmaster Tools, Microsoft SNDS. If reputation dips, pause and investigate before resuming.
Watch complaint rates. Stay under 0.05% during warmup. Above 0.1% and you are damaging the IP rather than warming it.
Authentication first. Do not start warming until DKIM, SPF, and DMARC are fully aligned. The first sends from a new IP are what mailbox providers use to learn your authentication posture.
Inbox OSS automates this entire process for dedicated IPs on Pro and Enterprise plans.