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:

A bounce happens when an email you send fails to reach the recipient. This is normal in cold email. Every sender gets bounces, and it does not mean something is broken. What matters is protecting your positive replies.

There are two types of bounces you might see.

Sender bounce. This happens when your inbox provider (Google Workspace, for the inboxes ListKit provides) 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.

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).

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.

Check your positive replies first. If they are falling, follow these four steps in order.

Pause all active campaigns for 48 hours. Open the Campaign page, open the menu next to your campaign, and choose 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:

{Hello|Hi|Hey} [first name]

Here [first name] is a placeholder for the first name variable: use the variables shown in the sequence editor.

The system randomly picks one option per send. Do this for your whole script (subject line and body), not just the greeting.

The easiest way to do this at scale is to use the AI spintax option in the sequence editor (100 credits), or paste your full script into an AI assistant like Claude or ChatGPT and ask it to add spintax to the whole thing.

For the full breakdown on syntax and best practices, see: How do I use spintax, including AI spintax?

No links anywhere in your email. Not in the body, not in the signature.

Open the Inboxes page from the sidebar, select all your inboxes, use the bulk option to update the signature, remove any links, and save.

Check your email body too. It's easy to leave a link in your copy by accident.

After the 48-hour pause and once the previous steps are complete, select all the inboxes your campaign uses and restart their ramp-up (see the screenshot below). Confirm when asked.

This sets the selected inboxes back to 1 email a day. Each inbox then adds 4 on each weekday it sends in a live campaign (1, 5, 9, 13, 17, 21, 25), so it reaches 25 a day on its 7th sending day, about 9 calendar days. It is the same ramp-up every new inbox goes through. You can't change the daily limit while an inbox ramps up.

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.

Following all four steps corrects the sending behavior that most commonly causes a bounce spike. Once your ramp-up completes again, your positive replies should recover toward 1 per 1,000 people contacted.

Triple verification checks the email format, the domain and mail server, and whether the mailbox exists, without sending a test email. This removes the vast majority of invalid addresses before they reach your campaign. It still can't prevent every bounce.

Verification is a snapshot in time. Between export and sending, things can change:

Sender bounces are a separate issue. They come from your sending pattern, not your list, so verification can't stop them. The 4-step protocol above fixes those. Remove hard bounces right away to protect your sender reputation.

If your positive replies are healthy, about 1 positive reply per 1,000 people contacted and a reply rate above 1%, bounce rate alone is not a problem.

How do I check my bounce rate?
Your bounce rate shows for each campaign on the Campaign page and in Analytics. Bounce numbers count bounce events, so they can be higher than the number of people who bounced. If your positive replies are falling, follow the protocol above.

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.

How long should I pause my campaign for?
48 hours. Do not send anything during this window.

What if my bounce rate is still high after following all 4 steps?
Send us a message in the app. Our support team replies Monday to Friday, 8am to 5pm ET. Messages sent outside those hours are answered the next business day. The team will look at your setup, including whether your lead data needs re-verification.

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.

What bounce rate is normal?
Bounce rate on its own does not matter. If you are getting about 1 positive reply per 1,000 people contacted and your reply rate is above 1%, ignore it and keep sending. Act only when replies fall.

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 looks higher. Is that a problem?
Pre-warmed inboxes can run a slightly higher bounce rate because they send from newer domains. Watch your positive replies. If those are healthy, keep sending.