How does inbox warmup work in ListKit?

THIS ARTICLE IS FOR: All ListKit customers
​Stage: Onboarding
​Owner: Said
​Last updated: July 2026
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Warmup is the foundation of everything in cold email. Without it, even the best copy sent to the most targeted list will land in spam. Understanding what warmup is and why it exists helps you set the right expectations from day one and make the most of the time before your campaigns go live.
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When a brand new inbox is created, it has no sending history. To inbox providers like Google, a new inbox that suddenly starts sending hundreds of emails per day looks suspicious, and suspicious behavior gets flagged, which means your emails go to spam before a single prospect ever reads them.
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Warmup solves this by gradually building a legitimate sending history for each inbox before you ramp up to full campaign volume. During warmup, your inboxes automatically send and receive a small number of emails each day through a warmup network. These emails are real sends that establish your inbox as a trustworthy, active sender in the eyes of inbox providers.
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Over 2 to 3 weeks, your inbox builds the reputation it needs to deliver cold emails reliably to the inbox, not the spam folder.
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Once your inboxes are created, ListKit starts warmup automatically. You do not need to configure anything or take any action.
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Behind the scenes, each inbox is exchanging emails with a network of other inboxes, sending, receiving, and engaging with messages in a pattern that mimics normal human email behavior. This signals to inbox providers that your inbox is legitimate, active, and trustworthy.
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The volume of these warmup emails starts low and gradually increases over the warmup period. By the time warmup is complete, your inbox has a solid sending history and is ready to handle cold email campaigns at full volume without triggering any flags.
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You can monitor the warmup status of each inbox from the Inboxes tab inside Email Engine at any time.

Minimum: 2 weeks
​Recommended: 3 weeks

These are not ListKit-specific timelines. They reflect how long inbox providers need to see consistent, legitimate sending behavior before treating an inbox as trustworthy. Every platform in the cold email industry, Instantly, Smartlead, and any other tool you might use, requires the same warmup period. There is no shortcut.
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The difference between 2 weeks and 3 weeks is deliverability headroom. At 2 weeks your inboxes are technically ready to send. At 3 weeks they have a stronger foundation, which means better inbox placement, healthier open rates, and a sender reputation that holds up better over time.
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Warmup does not stop when your campaigns launch, it runs continuously in the background alongside your live campaigns. This is intentional. Keeping warmup active helps maintain your sender reputation over time, not just build it in the beginning.
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You can enable or disable warmup per inbox from the three dot menu on any inbox inside Email Engine. However, turning it off is not recommended. Warmup running in the background is one of the things keeping your deliverability healthy month after month.

This comes up often, especially from customers who are eager to start sending as quickly as possible. The honest answer is that skipping warmup does not save time. It creates problems that take far longer to fix than the warmup period itself.
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An inbox that skips warmup and sends at full volume immediately will trigger spam filters. Once that happens, your sender reputation is damaged and recovering it means pausing campaigns, re-warming inboxes, and waiting anyway, except now you have already burned through part of your list and potentially flagged your domains.
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Warmup is not a ListKit policy. It is how cold email works everywhere on earth. The 2 to 3 week wait is the price of doing it right, and doing it right means your campaigns perform from day one instead of spending the first month fighting deliverability problems.
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You are not just waiting. From day one you have access to the Dream 100 Launch Bonus, a training and up to $100 in gift cards to help you start booking meetings from your main inbox while your sending inboxes warm up.
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You also have the Cold Email Mastery Course available in the Education section of your dashboard, the warmup period is the perfect time to go through it so you are fully prepared when your campaigns launch.
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​See: What is the Dream 100 bonus and how do I use it?
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After 2 to 3 weeks of warmup, your inboxes have a solid sender reputation, healthy deliverability scores, and are ready to send cold email campaigns at full volume. Emails land in the inbox, open rates start strong, and your sender reputation is protected for the long term.
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Does warmup start automatically or do I need to set it up?
It starts automatically once your inboxes are created. ListKit handles the entire warmup process in the background, no action required from you.
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Can I send cold email campaigns while my inboxes are warming up?
No. Your warming inboxes are not ready to send campaigns until warmup is complete. However you can run Dream 100 outreach from your main business inbox in the meantime, see: What is the Dream 100 bonus and how do I use it?
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What happens if I turn warmup off after my campaigns launch?
Your sender reputation may gradually weaken over time without the ongoing warmup activity running in the background. It is strongly recommended to keep warmup enabled at all times.
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My inboxes have been warming up for over 3 weeks, why are they not showing as ready?
Reach out to support via Intercom chat or at [email protected] and the team will check the status of your warmup and advise on next steps.
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Is warmup the same on every cold email platform?
Yes. The warmup requirement is universal across the entire cold email industry. Every platform requires it and the timeline is the same regardless of which tool you use.