Hi, I'm Maxime. I look after deliverability at lemlist, which mostly means I think about spam folders all day so you don't have to.

For a long time, lemlist showed you a "Deliverability score". A green circle and a number out of 100. Easy to read.

Too easy, it turned out.

One support message comes back again and again: "My deliverability score is 95, so why are my campaigns landing in spam?" The math behind the score was fine. The name promised something the score never measured.

So we changed two things. The score is now called Warmup Score, and you can finally see how we build the number. By the end of this article, you'll know what your Warmup Score measures, how we calculate it, and what to do when it drops to 70.

I know the usual journey by heart, because most of our customers follow it. You buy domains. You create mailboxes. They're brand new and nobody knows them yet, so you turn on warm-up.

A quick reminder of what warm-up is: neutral emails sent between real mailboxes, so mailbox providers learn to trust your mailbox and your domain. Google and Microsoft together hold about 80% of the market, so they are the two you need to convince. They want to see that the mailbox exists, that your volume stays reasonable (around 30 to 40 emails a day), and that your reputation is legitimate. If you're starting from zero, our lemwarm setup guide walks you through the ramp-up.

During this phase, the score behaves. It goes up, you wait, you watch it go up. Nobody opens a support ticket about a number that keeps rising.

Then you launch your first campaign and start sending real content. Real content is far less neutral than warm-up, and sometimes it's badly done. The same generic message goes to hundreds of leads. Nobody verified the list, so the bounces pile up. Recipients click "Report spam".

Meanwhile, warm-up keeps running in the background. Same mailbox, same domain, same Google and Microsoft watching.

Providers don't keep one filter for your campaigns and a separate one for your warm-up. They judge you as one sender. So if your outreach hurts your reputation, your warm-up emails start landing in spam too.

At that point, warm-up has nothing left to warm. It works more like a thermometer that shows you what your outreach is doing to your reputation.

This is where the old name misled people. "Deliverability score" sounded like an overall grade for how your campaigns get delivered. The score measures something narrower: how much providers trust you as a sender, seen through your warm-up emails. So we called it Warmup Score. I wish we had picked that name on day one.

A better name sets the right expectation. It still doesn't tell you why your score goes up or down. That's what we fixed next.

The score adds up four criteria:

The first three are technical checks. Once you set them up, they barely move. (If authentication is costing you points, start with our SPF, DKIM and DMARC setup guide.) Inbox rate is different. It changes every day, so that's where my team spent most of its effort.

The first change: you now see the breakdown wherever the score appears. Hover over it and you get the points for each criterion.

You get the full detail in lemwarm.

And the same view sits in your mailbox settings, right next to your warm-up settings.

The second change: we no longer calculate the score on a single day. Reputation builds over time, so we look at the last two weeks. That window is long enough to show a trend and short enough to reflect where you stand today.

A real case from our users. The mailbox has authentication in place, no blacklist, and a domain older than 30 days. But 20% of its warm-up emails land in spam. That gives it 0 out of 30 for inbox rate, and a final score of 70.

A lot of people see that 70 and assume the mailbox is burned. It isn't. 20% in spam means 80% in the inbox. I agree that's not good enough, but a dead domain looks very different. A 70 tells you that providers found reasons to be suspicious of you, like generic content, a low-quality list, or spam reports.

This is the moment you take back control. A score is a summary, and a summary hides details. Look at the actual spam rate, find where it comes from, and fix the cause instead of the symptom. That's what recovery means. Run your copy through our spam words checker and verify your list with the email verifier before your next send. If bounces are already piling up, our guide on reducing email bounces is a good first stop.

I still like this number. It gives you a lot of information in one glance. It can't give you the whole story, though, and after reading so many tickets about it, I'd rather you know that from the start.

So the next time your Warmup Score drops to 70, don't panic. Open the breakdown, check your inbox rate, and look at your last campaigns. If you're not running warm-up on your mailboxes yet, see how lemwarm works.