If you’ve ever set up a new Klaviyo account, you’ve probably heard the rule: warm up your domain before you start sending at full volume. But domain warm-up is not a one-and-done rite of passage. If your open rates have been sliding, deliverability feels off, or you just cleaned your list and changed your sending patterns, a warm-up might be the reset your account needs.

What Domain Warm-Up Actually Does (And Why It Still Matters)

Domain warm-up is how you build trust with inbox providers. Instead of blasting your full list, you start by emailing the subscribers most likely to engage, then gradually expand your audience in stages.

That staged approach sends a simple message to Gmail, Yahoo, Apple Mail, and everyone else: your emails are wanted. People open them. People click them. You’re a legitimate sender.

This is why warming up your domain is useful for brand-new senders. It’s also why it works as a reset when performance has declined.

Warm-Up Is Not Just for New Domains

Most brands file warm-up under “something you do at setup.” Then they never think about it again.

The problem is that your sending conditions change over time:

• Open rates drift downward
• Engagement drops as your list ages
• Your list gets cleaned and your audience composition changes
• You stop sending consistently, then start again
• You ramp volume up quickly around launches

When those conditions shift, inbox providers reassess you. Warm-up is one of the cleanest ways to course-correct, especially if things feel subtly “off” and you don’t want to wait for a full-blown deliverability crisis.

The Open Rate Threshold That Should Get Your Attention

When I’m auditing a Klaviyo account, there’s one benchmark that gets my attention fast.

Use 20% as Your “Investigate This” Line

• If your open rates are consistently below 20%, something is worth investigating.
• Below 15%, something is almost certainly wrong.

Those numbers often mean inbox providers are making decisions about your emails before your subscribers ever see them. And the longer that pattern continues, the harder it is to recover.

Check Authentication Before You Warm Up

Before you jump into warm-up, check your foundation: authentication.

Specifically:

• DKIM
• SPF
• DMARC

These records help inbox providers verify that emails coming from your domain are actually from you. If authentication is broken or misconfigured, warm-up alone won’t address the underlying issue.

Warm-up works best when your technical setup is solid and you’re trying to rebuild engagement signals.

When a Warm-Up Makes Sense (Even If You’ve “Already Done One”)

Warm-up is worth considering when:

• Your open rates have been declining for months
• Deliverability feels inconsistent or unpredictable
• You paused sending for a while and are restarting
• You just completed a major list clean
• You are ramping volume back up after a shift in strategy

If you listened to the list health episode, this is the natural next step. Cleaning your list resets your audience. Warm-up is how you rebuild sender reputation on top of that cleaner foundation.

How to Run a Warm-Up Campaign in Klaviyo (Phased Sends)

A warm-up is not one big send. It’s a series of smaller sends, each one expanding outward from your most engaged segment.

Here’s what it looks like in practice.

Step 1: Start With Your Most Engaged Segment

Choose a segment with a high likelihood of positive engagement. For many accounts, that’s something like:

• Clicked in the last 30 days

Send your campaign to that group first.

Step 2: Expand in Stages Without Double-Sending

Then duplicate the campaign and expand your audience, while excluding anyone who already received the earlier phase. For example:

• Phase 1: Clicked in the last 30 days
• Phase 2: Clicked in the last 60 days (exclude Phase 1 recipients)
• Phase 3: Clicked in the last 90 days (exclude Phase 1 + 2 recipients)

This protects engagement signals. It also makes your warm-up data cleaner.

Step 3: Wait Long Enough to Collect Real Data

Patience is not optional here. Give each phase time to breathe.

In most cases, that means waiting at least 48 hours between phases (sometimes longer, depending on list size and engagement patterns). If you rush, you don’t get reliable signals, and you risk compounding the problem you’re trying to fix.

Step 4: Use Checkpoints Before You Expand Further

Between each phase, look at your core signals:

• Open rate
• Click rate

If a phase comes back under a 15% to 20% open rate, that’s your cue to pause and reassess before widening the audience.

Warm-up works because it’s staged. Those checkpoints are the whole point.

The Biggest Warm-Up Mistake: Rushing It

Most brands want warm-up to be quick. They do one small send, it looks fine, and they immediately jump to a much bigger audience.

That impatience is how warm-up fails.

Warm-up only works when you’re willing to collect data, adjust, and expand slowly. Otherwise, you’re just speeding into the same deliverability wall with a different strategy label.

Warm-Up and List Health Go Together

List health and warm-up are two sides of the same fix.

A list clean removes dead weight and risky profiles. But that cleanup can also change your engagement patterns and sending behavior dramatically. Warm-up is how you rebuild trust after that shift, using your most engaged subscribers to lead the way.

One without the other is often only half the solution.

When to Get Help (Because the Details Matter)

You can absolutely learn warm-up on your own, but this is one of those areas where details make a real difference:

• Segmentation logic
• Exclusion rules
• Timing between phases
• Knowing what to watch and when to pause

If you’re dealing with deliverability issues and you want a clean reset, warm-up can work. It just needs to be done carefully.