Fix duplicate emails and semicolon delimiters in a Mailchimp CSV

Decide whether the problem is duplicates or separators

Mailchimp checks imports for duplicates, syntax errors, unsupported formats, and semicolons used instead of commas. A duplicate email is counted once in an audience, while a semicolon file can stop field mapping before import. Handle these as two explicit branches.

• The same email appears more than once: remove duplicates using the email column.
• Columns are not separated in the preview: convert the confirmed semicolon delimiter to commas.
• An address is malformed or role-based: review Mailchimp's import history; do not invent a replacement address.

• Remove duplicate records before importing →Check duplicate IDs or email addresses before you create a second record.
• Convert the CSV encoding or delimiter →Choose the source and output format explicitly before the destination import.
• Fix duplicate emails before a Mailchimp import →Remove repeated addresses locally, then review Mailchimp's import history.

Inspect the email column and delimiter first

Open a copy of the export as text and identify the email header. Confirm whether fields are separated by commas or semicolons; a comma inside a quoted name is not a delimiter. Keep the original export so a rejected import can be undone or retried with a different branch.

• Mailchimp's contact import requires one email address column for email contacts.
• Whitespace and typos can cause syntax errors even after duplicates are removed.
• If the source is over 200MB or around one million contacts, split it into smaller imports according to Mailchimp's guidance.

• Find CSV rows with inconsistent column counts →Diagnose malformed rows before uploading them to a platform.
• Learn the general CSV split workflow →Choose a row count or target size while keeping the header in every output file.
• Keep only the CSV rows you need →Filter test, inactive, or incomplete records before the import.
• Diagnose quoted newlines before a Jira import →Check record boundaries and the required Summary header before mapping fields.

Remove repeated emails in LocaCSV

LocaCSV does not send contact values to a server. It also does not validate consent, subscription status, or whether an address is deliverable; those decisions stay with Mailchimp and your compliance process.

1. 1Save the Mailchimp export as an untouched backup and open its copy in the duplicate-removal workspace.
2. 2Select the email column as the key instead of comparing unrelated profile fields.
3. 3Run the operation and keep the first row for each email in input order.
4. 4If the file uses semicolons, open format conversion next and select comma as the output delimiter after checking the preview.

Match the local result to Mailchimp's import history

• The output contains one row per selected email key, with the intended first record retained.
• The total is input rows minus removed duplicates; no unrelated rows were silently changed.
• The output delimiter is comma and quoted names containing commas still occupy one field.
• Mailchimp's import history shows added, updated, skipped, and syntax-error counts that you record separately.

• Convert the CSV encoding or delimiter →Choose the source and output format explicitly before the destination import.
• Find CSV rows with inconsistent column counts →Diagnose malformed rows before uploading them to a platform.

Handle the next Mailchimp error by its cause

If the import still skips contacts, inspect syntax errors, role-based addresses, unsubscribes, and the audience's Auto-Update setting. Do not remove rows only because Mailchimp reports them as unsubscribed; that is an audience decision, not a CSV formatting fix.

• Convert the CSV encoding or delimiter →Choose the source and output format explicitly before the destination import.
• Find CSV rows with inconsistent column counts →Diagnose malformed rows before uploading them to a platform.
• Diagnose quoted newlines before a Jira import →Check record boundaries and the required Summary header before mapping fields.

Import a contact list you can reconcile

Upload the separate, deduplicated CSV to Mailchimp, compare the import history with the local counts, and keep the rejected-address report with the campaign record.