How to clean a Klaviyo list before your next flow

To clean a Klaviyo list, export the list or segment as a CSV, verify every address, then suppress the undeliverable profiles and write the verdict back as a profile property so you can build a segment of verified-deliverable profiles for campaigns and flows. Verifyre's Klaviyo integration does the whole loop in one click: it pulls the list, verifies it and pushes the results back as properties or suppressions.

Profiles, lists and segments

Klaviyo is built around profiles, not lists. A profile is one person with an email address, properties and an event history. A list is a static membership that a profile joins by opting in or being imported. A segment is dynamic: Klaviyo evaluates its conditions continuously and profiles move in and out on their own.

Suppression sits above all of that. A suppressed profile receives nothing, from any list, segment, campaign or flow, until it is unsuppressed. This is the lever you want for undeliverable addresses, because it stops every send at once rather than just removing someone from one list.

The practical consequence: you clean profiles, not lists. Verify the addresses, mark the profile, and let segments do the sorting.

Why bounces hurt flows differently from campaigns

A campaign is one send to a defined audience. If 3% of it bounces, you get one bad day, a warning from Klaviyo, and a dent in your reputation that you can see and fix.

Flows are different. A welcome series, an abandoned cart flow or a post-purchase flow triggers on events and sends one profile at a time, all day, every day. A bad address collected on your sign-up form this afternoon bounces in your welcome flow tonight. Tomorrow's bad addresses bounce tomorrow night. The bounce rate never spikes; it drips, and because the drip is constant it quietly shapes how Gmail and Yahoo see your domain. Flows also carry your most valuable messages, so a throttled flow costs revenue, not just opens.

Klaviyo suppresses hard bounces automatically, which limits the damage, but each one has already been counted against you by the receiving provider. The goal is to stop the bounce from happening at all.

Step 1: export and verify

From the list or segment you want to clean, export the profiles as a CSV with the email column and any properties you want to carry across. Upload it to the bulk email verifier. Each address gets a syntax check, an MX lookup, a real SMTP handshake, a catch-all probe for its domain, disposable and role detection, a score from 0 to 100 and one of four verdicts: deliverable, undeliverable, risky or unknown. Duplicates and malformed addresses are free.

If you would rather skip the spreadsheet, connect the Klaviyo integration. It pulls the list, verifies it, and writes the results back to each profile as properties, with the option to suppress undeliverable profiles automatically. Run it again before the next big campaign and it only spends credits on new or stale addresses.

Step 2: suppress undeliverable profiles

Take the undeliverable file and add those addresses to Klaviyo's suppression list. Klaviyo accepts a CSV upload of email addresses to suppress, so this takes a minute. Do not delete the profiles: deleting throws away purchase history, event data and consent records, and if the person signs up again you start from zero. Suppression is reversible, deletion is not.

If you are using the integration, choose "suppress undeliverable" and this step is done for you.

Step 3: build a verified-deliverable segment

Import the deliverable file back into Klaviyo with "update existing profiles" so that each profile gets two custom properties: a verification status (deliverable, risky, unknown) and a verified-at date. The integration writes the same properties.

Now create a segment: verification status equals deliverable, verified-at is within the last 180 days, and the profile can receive email marketing. Use that segment as the audience for campaigns, and add the same conditions as a flow filter on the flows that matter most. Everyone outside the segment is still a profile, still accumulating history, just not being mailed until they are verified.

Step 4: decide on risky and unknown

Risky profiles are usually on catch-all domains or are role addresses such as info@ or sales@. A catch-all domain accepts mail for any address, so no verifier can prove a specific mailbox exists. Our advice: let risky profiles stay in flows, where a bounce here and there is absorbed, but exclude them from large campaigns unless they have opened something in the last six months. The catch-all checker shows which domains behave this way.

Unknown means the receiving server did not answer clearly. Re-verify after a day or two; most resolve to deliverable or undeliverable. Anything still unknown after three attempts is treated as risky.

Role addresses deserve a separate thought. They are often shared inboxes with no single owner and are among the most likely to mark you as spam. Our role email checker flags them, and the role-based addresses post explains when to keep them.

Step 5: keep the forms clean

A cleaned list is only as good as what enters it next. On sign-up forms you control on your own site, the form validation widget checks the address as it is typed: syntax, typo suggestions, disposable and role detection, an MX check and an optional live mailbox check, all before the form submits. For sign-ups that come through channels you cannot put a widget on, call the email verification API when the profile is created and set the verification property before the welcome flow fires. A flow filter on that property then keeps the first email from bouncing.

Measuring the result

Compare the 30 days before and after: bounce rate on the welcome flow, bounce rate on the next full campaign, the share of new profiles landing in the verified-deliverable segment, and your spam rate in Google Postmaster Tools. The welcome flow number is the one to watch, because it reflects what your forms are letting in today. Our bounce rate calculator gives you a quick read on where you stand.

What to do next

Export the list you send to most, verify it with the bulk email verifier, suppress the undeliverable file and build your verified segment. Or connect the Klaviyo integration and do it in one step. New accounts get 100 free credits, enough to verify a sample and see the verdicts before you run the full list. The list hygiene checklist covers the ongoing routine.