Our team recorded a full video walking through this exact protocol, showing each step live inside ListKit. Watch it here if you prefer to follow along visually:
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A bounce happens when an email you send fails to reach the recipient. This is completely normal in cold email, every sender experiences bounces, and it does not mean something is broken. What matters is keeping your bounce rate under control.

There are two types of bounces you might see.
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Sender bounce. This happens when your inbox provider, Google, in ListKit's case, blocks the email before it even leaves your inbox. Google does this when it detects a pattern in your sending behavior, usually because the same email copy is going to too many people without variation, or because your inboxes are sending at too high a volume too quickly. This has nothing to do with your leads, they are still valid. It is a sending behavior issue and it is fully fixable.
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Hard bounce. This happens when the lead's email address is invalid, the address does not exist or has changed since it was verified. Even with triple verification, email addresses can become invalid quickly because people change jobs, companies shut down, and inboxes get deleted. This is why re-verifying older lists with the Email Verifier before you reuse them is good practice (1 credit per email).
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Both types of bounces are a normal part of cold email. The goal is not zero bounces. It is protecting your positive replies, and fixing bounces quickly when a spike comes with falling replies. The protocol below focuses on correcting your sending behavior, which is the most common and most fixable cause of a bounce spike.
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Check your positive replies first. If they are falling and your bounce rate is 5% or more, follow these four steps in order.
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Pause all active campaigns for 48 hours. Go to Campaigns, click the three dots next to your campaign, and hit Pause. Do not send anything for two full days.

Spintax sends variations of your email so Google does not see the exact same message going out to thousands of people. It looks like this:
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{Hello|Hi|Hey} {{first_name}}
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The system randomly picks one option per send. Do this for your whole script (subject line and body), not just the greeting.
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The easiest way to do this at scale is to copy your full script, paste it into Claude or ChatGPT, and ask it to spintax the whole thing for you.
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For the full breakdown on syntax and best practices, see: How do I use spintax in ListKit?
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No links anywhere in your email. Not in the body, not in the signature.
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Open Inboxes from the left sidebar, tick the checkbox at the top of the list to select all inboxes, open the bulk actions, click Update Signature, remove any links from the signature, and save.
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Check your email body too. It's easy to leave a link in your copy by accident.
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After the 48-hour pause and once the previous steps are complete, go to your campaign, click Select All on your inboxes, and click Restart Ramp-Up. Confirm by clicking I understand my sending limits.
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This resets sending to 1 email per inbox per day, adding 4 per day until it reaches the full 25 per inbox per day on day 7, the same ramp-up schedule used when your inboxes are first set up. You can't change the limit manually while it ramps up.
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Do not skip this step and jump straight back to full volume. Sending at full volume immediately after a bounce spike is what caused the issue in the first place, the ramp-up gives your inboxes time to rebuild trust with Google gradually.
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Following all four steps corrects the sending behavior that most commonly causes a bounce spike. Once your ramp-up completes again, your bounce rate should return to a healthy range under 5%.
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How do I check my bounce rate?
Open Campaigns or Analytics from the left sidebar. Both show a Bounce column for each campaign. If it is 5% or higher and your positive replies are also falling, follow the protocol above.
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Do I need to do all 4 steps, or can I skip some?
Do all four. The protocol is designed to correct your sending behavior comprehensively, skipping steps may mean the underlying issue is not fully resolved.
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How long should I pause my campaign for?
48 hours. Do not send anything during this window.
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What if my bounce rate is still high after following all 4 steps?
​Reach out to support via the chat icon at the bottom right of your dashboard, or tag the team in the ListKit Slack community. They will investigate your specific setup, including checking whether your lead data needs re-verification.
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Why does restarting ramp-up matter so much?
Jumping straight back to full sending volume after a bounce spike repeats the exact behavior that triggered Google to flag your inboxes in the first place. The gradual ramp-up rebuilds trust with the inbox provider over several days.
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Is a bounce rate under 5% considered normal?
Yes. 2 to 4% is typical. Even above that, bounce rate alone is not a problem if your positive replies per 1,000 people contacted are healthy. Act when bounces rise and replies fall.
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What falls under a hard bounce vs a sender bounce?
A hard bounce means the lead's email address itself is invalid. A sender bounce means Google blocked the email due to your sending pattern, even though the lead's email may be perfectly valid. This protocol focuses on correcting sending behavior, which resolves the most common cause of a spike.

I use pre-warmed inboxes and my bounce rate is around 4 to 5%. Is that a problem?
Pre-warmed inboxes run a slightly higher bounce rate (about 4.4% on average) because they run on newer domains. Watch your positive replies. If those are healthy, keep sending.