What is IP warmup?

IP warmup is the process of gradually increasing your sending volume from a new IP address so mailbox providers like Gmail and Outlook learn to trust you. When an IP has no sending history, providers don't know if you're a legitimate sender or a spammer. They start by accepting only small volumes (sometimes just a few hundred emails per day) and watch how recipients react. Low complaint rates, good engagement, and clean authentication prove you're legit. As that proof builds, they gradually lift the limits.

Why the slow ramp? Mailbox providers use IP reputation as a core filtering signal. A brand new IP has zero reputation, which makes it look like every other new IP that spammers spin up every day. If you try to send 50,000 emails on day one from a fresh IP, providers assume you're a spammer and block you or route everything to spam. The warmup process mimics natural sender behavior (starting small, building engagement) so providers learn your IP sends mail people actually want.

But Here's what a typical warmup schedule looks like. Day 1: 50-100 emails. Day 2: 100-200. Day 3: 200-500. Day 4: 500-1,000. You keep doubling every few days until you hit your target daily volume. The exact schedule depends on your engagement rates. If recipients are opening, clicking, and not complaining, you can accelerate. If you see bounces or spam complaints, slow down or pause. Most ESPs that offer dedicated IPs (like SendGrid, Mailgun, Klaviyo) have built-in warmup tools that automate this schedule for you.

The hardest part of warmup isn't the schedule, it's making sure your first emails perform well. Send to your most engaged subscribers first. These are people who've opened or clicked in the last 30 days, ideally people who signed up recently and are expecting your emails. Don't send to cold lists, purchased lists, or old unengaged contacts during warmup. One spike in complaints or bounces during warmup can tank your IP reputation before it even gets built.

Authentication is non-negotiable during warmup. You need SPF, DKIM, and DMARC configured correctly before you send a single email. Providers won't trust an unauthenticated IP no matter how slowly you warm it. Check your setup with our free SPF checker and DKIM lookup before you start.

One more thing: warmup applies to NEW IPs only. If you're on a shared IP pool (which most small senders are), the IP is already warmed. Your ESP handles that. You only need to worry about warmup if you're migrating to a dedicated IP or setting up your own sending infrastructure.