How do I perform an IP/domain warmup?

You've got a shiny new IP address or domain, and you're ready to send. The temptation is to load up your full list and hit go. Don't. Mailbox providers like Gmail and Outlook have never seen you before, and a stranger showing up with 500,000 emails on day one looks a lot like a spammer. A warmup is how you prove you're not one.

The whole idea is to build sender reputation gradually. Mailbox providers track engagement patterns over time. When they see consistent, small volumes of mail that people actually open, they start to trust you. That trust is what gets your later, larger sends into the inbox.

Before you send a single email, your foundation needs to be solid. SPF, DKIM, and DMARC all need to be set up correctly. Warming up without authentication in place is like building on sand. You also want your list segmented by engagement before you start.

Step 1: Start small, send to your best people

Depending on your total list size, start with somewhere between 50 and 500 emails on day one. These should go to your most engaged subscribers, the ones who open consistently, click regularly, and have heard from you recently. Their positive engagement signals (opens, clicks, replies) are what train mailbox providers to trust your sending address. Don't waste your warmup sending to cold or stale contacts first.

Step 2: Increase volume steadily

A rough guide is to double (or increase by 50 to 100 percent) every one to three days, as long as your metrics stay healthy. The full warmup typically takes two to four weeks to reach your target volume, though larger lists or dirtier reputations can take longer. There's no magic number. Typical warmup schedules exist as starting points, not gospel.

Step 3: Watch your signals daily

During warmup you need to check three things every single day. Bounce rates, complaint rates, and open rates. If your hard bounce rate climbs above one percent, stop and clean your list. If complaint rates rise above 0.1 percent, slow down and look at who you're sending to. Soft bounces and deferrals (especially at Gmail) are a sign the mailbox provider isn't sure about you yet. Slow down, don't push through.

Postmaster Tools from Gmail and Smart Network Data Services (SNDS) from Microsoft let you see your reputation score directly. Set these up before your first send, not after something goes wrong.

Step 4: Gradually bring in less-engaged subscribers

But once your metrics look stable at a given volume, add your next engagement tier. Mid-engaged subscribers come next, then lower-engagement contacts, then the oldest or least-active ones last. If you segment your list during warmup properly, you're essentially stacking positive signals before the riskier sends go out.

Step 5: Know when to pause

But if you hit a wall, high bounces, deferrals piling up, reputation dropping in postmaster tools, pause. Don't keep pushing. Drop back to a lower volume for two to three days, let things stabilize, then resume the ramp. Forcing volume through a bad signal window is one of the most common warmup mistakes people make.

Warmup is a patience game (one that pays off). Done right, you come out the other side with a clean reputation that actually holds up under real sending volume. Rush it and you'll spend weeks trying to recover from a reputation hole you dug yourself.

If you're not sure where your domain reputation currently stands, our free blocklist checker is a quick first look. And if you're mid-warmup and something's going sideways, the SOS hotline is free. We actually pick up.