Bad lists burn sender reputation.

Duplicate contacts get double emails, blank rows fail the import, and '[email protected] ' and '[email protected]' become two subscribers. Before the list touches Mailchimp, Klaviyo, Brevo, or your CRM, run it through CSV Power Editor: merge sources, normalize, dedupe by email, and filter the junk — locally, without uploading your list to yet another service.

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Clean Email Lists Before You Import — illustration

Workflow

Raw signups to import-ready list.

1

Gather and merge the sources

Open the first export and import the rest as tabs — webinar signups, lead magnets, store exports, partner lists. Run Merge Files to combine them into one sheet with a preview before applying.
2

Normalize the email column

Trim Spaces kills invisible whitespace and Change Case lowercases everything, so formatting variants of the same address become identical before matching.
3

Dedupe by email

Remove Duplicates keyed on the email column collapses repeat signups. Check Fuzzy Duplicates afterward for typo variants worth a human look.
4

Filter out the junk

Use filters to drop rows where email is blank, and the regex operator to flag rows that don't look like addresses at all. Live counts show how much each rule removes.
5

Flag unsubscribed addresses

Export your suppression or unsubscribe list and run Compare Files keyed by email — matches are addresses on both lists, which you review and exclude before import.
6

Export clean UTF-8 CSV

Save As writes a UTF-8 CSV with correct quoting that import wizards accept without column-mapping surprises. Save Filtered exports only the visible rows if you carved a segment.

Why it works

Hygiene is structure, done in order.

Normalize before dedupe

Most duplicate subscribers are casing and whitespace variants. Trimming and lowercasing first means key-based dedupe catches them all in one pass.

Pattern filtering with regex

The filter bar's regex operator isolates rows with malformed addresses — missing @, spaces inside, trailing punctuation — so they're reviewed instead of bouncing.

Suppression awareness

Comparing against your unsubscribe export keyed by email surfaces re-imported opt-outs before they become a compliance problem, with the overlap documented in a reviewable workbook.

Your list stays yours

Email lists are personal data. Everything runs locally on your Mac — no list uploaded to a cleaning service, no third party added to your privacy policy.

FAQ

Common questions.

Does it verify whether addresses are deliverable?

No. It cleans the structure of the list — duplicates, blanks, casing, malformed patterns, suppression overlap. Deliverability verification (does the mailbox exist) requires an email-verification service; doing both gives the best result.

How do I stop '[email protected]' and '[email protected]' from importing as two contacts?

Run Change Case to lowercase the email column and Trim Spaces to remove whitespace, then Remove Duplicates keyed on email. The variants collapse into one row.

Can I combine lists from several sources first?

Yes. Import each CSV or XLSX as a tab, run Merge Files to combine them, then dedupe the merged sheet — overlap between sources is exactly where duplicates come from.

How do I respect my unsubscribe list?

Export the suppression list and run Compare Files keyed by email. Addresses present in both lists are identified in the compare workbook so you can exclude them before importing.

Will the cleaned file import into Mailchimp or Klaviyo?

Yes. The export is a standard UTF-8 CSV with proper quoting, which is what those import wizards expect. Headers stay as you see them in the grid.

Is my list uploaded anywhere?

No. The app runs entirely on your Mac with no outbound network connections.

Keep going

Bad lists burn sender reputation.

Raw signups to import-ready list.

Gather and merge the sources

Normalize the email column

Dedupe by email

Filter out the junk

Flag unsubscribed addresses

Export clean UTF-8 CSV