By Nikoleta Zoric, Email Expert 

We just wrapped a re-warm for a brand going through a full rebrand, and it worked exactly as it should. Reputation held, list held, launch landed. It’s the kind of project we’ve run dozens of times now, but it’s still fresh. And we want to talk about it because we keep watching business owners and operators tweak their sender settings without a second thought for what it does to their reputation.

Sender address changed from hello@ to team@. ESP migrated over the weekend. Two months of silence were broken with a big Black Friday campaign. Domain swapped in a single afternoon for a rebrand. Each one is a sender reputation event. Nobody in the room ever calls it that.

Gmail, however, does. And since February 2024, the consequences of getting it wrong have become a lot more expensive.

So let’s talk about re-warming. What it is, why you need it, when you need it, and what it actually looks like when you run one.

What Is Re-Warming?

Re-warming is the deliberate process of rebuilding your sender reputation after it’s been damaged, paused, or reset. You send less, more consistently, to the people most likely to want it. Done properly, it takes six to eight weeks.

The mechanics are simple. Inbox providers like Gmail, Yahoo, and Outlook build a reputation on your sending domain over time. That reputation decides whether you land in the Primary inbox, in Promotions, or in spam. Anything that disrupts your normal sending pattern puts that reputation at risk: a new domain, a long silence, a sudden volume spike, a wave of spam complaints. Re-warming is what you do to rebuild it.

Why You Need It (And Why the Stakes Just Went Up)

Gmail’s February 2024 bulk sender rules got real teeth in November 2025. The hard spam complaint threshold is now 0.3% per campaign. Cross it once and Gmail starts filtering you on that send and every one after. Healthy is 0.1%. Yahoo adopted the same standard.

In practice, this means one sloppy send can drag your next month of campaigns into Promotions. A worse one lands you in spam. The margin for casually shuffling sender identity has shrunk overnight, and we haven’t met a founder in the past year who realized this was happening to them.

The good news: the play that fixes it isn’t a secret. It’s built into Klaviyo. When your deliverability score drops below 50, their Reputation Repair AI kicks in and restricts your sends to a phased engagement window: 30 days first, then 60, then 90, then 120, widening as your score recovers. That’s a re-warm by another name. The bad news: by the time Klaviyo’s doing it for you, you’re already weeks into a revenue dip you didn’t see coming.

When You Need to Run One

There are proactive triggers and reactive ones. The proactive triggers give you a planning window and cost nothing extra if you plan for them:

• You’re rebranding with a new domain, sender name, or identity
• You’re switching ESP
• You’ve gone silent for six or more weeks and want to come back
• You’re inheriting a list from an acquisition or partnership

The reactive triggers mean something has already gone wrong and you’re playing catch-up:

• Your open rate has dropped well below 20% (ecommerce average is 25 to 38%)
• Your Klaviyo deliverability score has slipped below 75 and isn’t recovering
• Your spam complaint rate has crossed 0.1% on recent sends
• Your Google Postmaster Tools reputation has dropped to Low or Bad
• Recent campaigns started landing in Promotions when they used to land in Primary

If any of the proactive triggers are on your calendar, plan for it. The window closes the moment you press send from the new setup. After that, you’re not planning anymore. You’re fixing.

What a Re-Warm Actually Looks Like

Here’s the shape of it, drawn from the rebrand we just wrapped. New name, new domain, new sending identity, a healthy list built over years under the old brand. If they’d migrated the list, switched the domain, and hit send on the launch campaign in one shot (the standard rebrand playbook), the launch would have failed. Sender reputation torched before the founder’s morning coffee.

Instead, we ran six phased sends over five weeks, expanding the audience deliberately:

• Send 1: warmest first. Suppressed anyone inactive 12 months or more. First re-warm went to the top 4,500 subscribers, the most engaged in the past 30 days. Open rate came in above 61%. That’s the signal you want going into a re-warm: your warmest audience showing up.

• Send 2: first expansion. Widened to around 11,000 recipients. Open rate held at 60%. Klaviyo deliverability score climbed, Postmaster reputation held.

• Send 3: further expansion. Widened to about 17,800 recipients. Open rate dropped to 38%. That was expected, since a lower engagement tier had come in. Held that audience for the next send to let engagement stabilize instead of expanding again.

• Sends 4 and 5: consolidation. Two more sends at similar audience size. Open rates recovered to 65% and 63%.

• Send 6: the launch expansion. Sent to nearly 54,000 recipients, the fully warmed list. Open rate landed at 56%, click rate above 1%, and the campaign generated over $6,600 in revenue on its own.

Six sends. Five weeks. A new sending domain that started at zero reputation and ended with a launch that outperformed anything the old brand had put out that quarter.

For context on what “healthy” actually looks like: Klaviyo’s current ecommerce benchmarks put open rates in the 25 to 38% range. This account’s trailing 30-day average is sitting at 61.5%, well above the top of that range. That’s a clear signal the sender reputation is now firmly in the “trusted” bucket. Sustained rates below 20% mean deliverability trouble. Anywhere in the 30s for a launch is a strong outcome. Above 55% on a broad send after a re-warm is genuinely exceptional.

The Question Worth Sitting With

What’s on your calendar in the next six months?

If any of it involves changing your domain, your sender name, your platform, or your sending cadence, email needs to be part of that conversation. Not the week before launch. Now.

The brands we work with who plan for this land their big moments cleanly. The ones who don’t spend the six months wondering why something feels off. Either way, you find out. The question is what it costs to learn.

Domain changes don’t deserve a grimace. They deserve a plan.

Planning a rebrand? Switching ESPs? Coming back from a long silence? This one’s for you.