You can import contacts into Mailchimp by uploading a CSV or TXT file, or by copying and pasting contact data directly into the platform. The process takes just a few minutes once your file is formatted correctly, but getting that formatting right is the step most people stumble on. Here’s how to prepare your data and walk through the import smoothly.
Prepare Your File
Mailchimp accepts CSV and TXT files only. It will not accept Excel (.xls or .xlsx), vCard (.vcf), ACT!, or other file types. If your contacts live in a spreadsheet, open it and use “Save As” to export it as a CSV before uploading.
The only required column is “Email Address.” Label it exactly that way in the first row of your spreadsheet. You can include as many additional columns as you want for first name, last name, phone number, birthday, mailing address, tags, or any custom fields you’ve created in Mailchimp. Just make sure each column has a header in the first row so Mailchimp knows what the data represents.
A few formatting rules to keep in mind before you save:
- Dates: Use the ISO standard format YYYY-MM-DD (like 2025-03-15) for any date field other than birthdays. For birthdays specifically, use MM/DD or DD-MM.
- Phone numbers for SMS: These must follow the E.164 international format, starting with a + sign, then a 1 to 3 digit country code, then the subscriber number (up to 12 digits). For a U.S. number, that looks like +15551234567.
- Mailing addresses: Use two-letter country codes instead of full country names. The United Kingdom, for example, must be “GB” rather than “UK.” Each line of the address must stay under 45 characters.
- Tags: Tag names can be up to 100 characters. If a tag contains a comma, wrap it in double quotes so Mailchimp doesn’t split it into two tags. For example: “Monday, Wednesday”. Emojis are not supported in tags.
- Text fields: Any text field maxes out at 255 bytes and will be clipped if it exceeds that limit.
- Semicolons: Some European spreadsheet programs use semicolons instead of commas to separate fields in CSV files. If yours does, find and replace all semicolons with commas before importing.
Upload Your File
Log into Mailchimp, navigate to the Audience section, and select the audience you want to import contacts into. Click “Add Contacts,” then choose “Import Contacts.” You’ll see the option to upload a CSV or TXT file, or to copy and paste your data directly. The copy-paste method works well for small lists of a few dozen contacts, but for anything larger, uploading a file is faster and less error-prone.
After you upload, Mailchimp will ask you to match the columns in your file to the corresponding fields in your audience. If your column headers match Mailchimp’s default field names (like “Email Address,” “First Name,” “Last Name”), it will auto-match them. For custom fields, you’ll need to map each column manually using the dropdown menus. This is also where you can assign tags to every contact in the import or place them into specific groups.
To add contacts to more than one group during import, separate each group name with a comma and a space in your file.
Set the Right Marketing Status
During the import process, Mailchimp asks you to confirm the marketing permission status for the contacts you’re bringing in. This matters because sending marketing emails to people who haven’t opted in violates both Mailchimp’s terms of service and anti-spam laws in most countries.
If your contacts explicitly signed up to receive marketing from you (through a signup form, a checkbox at checkout, or a similar opt-in mechanism), you can import them as subscribed contacts. If they haven’t given that permission, import them as non-subscribed. Non-subscribed contacts are stored in your audience and can receive transactional emails, but they won’t receive your marketing campaigns until they opt in.
Why Contacts Get Skipped
After an import finishes, Mailchimp shows a summary with the number of contacts added, updated, and skipped. If your numbers don’t match what you expected, a few common causes explain the gap.
Syntax errors are the most frequent issue. Mailchimp rejects any email address that’s malformed or incomplete. That includes addresses missing a “.com” or another domain extension, addresses with extra spaces before, after, or in the middle, typos in common domains (like “gamil.com” or “yhoo.com”), and addresses containing unsupported UTF-8 encoded characters in the part before the @ sign.
Role-based addresses like sales@company.com, info@company.com, or support@company.com are automatically removed during import. Mailchimp strips these because they typically belong to a department rather than an individual, and sending marketing email to them tends to generate spam complaints.
If duplicate email addresses appear in your file, Mailchimp imports the contact once and updates the profile with the most recent row of data. This is normal behavior, not an error, but it means your total imported count will be lower than the number of rows in your file.
File Size Limits
Your CSV or TXT file can be up to 200MB, which accommodates roughly one million contacts. Files larger than that may cause import errors. If you have a list that exceeds this limit, split it into multiple files and run separate imports.
Also check the OPTIN_TIME or CONFIRM_TIME columns if your file includes them. These timestamps record when a contact originally subscribed. If any dates are set in the future, the import will fail. This sometimes happens when exporting from another email service provider that formats dates differently.
Importing From Other Platforms
If you’re migrating from another email marketing platform, export your list as a CSV from that service first. Files exported from other providers sometimes use non-standard formatting, so open the CSV in a spreadsheet program and verify that the columns look clean before uploading to Mailchimp. Make sure email addresses are in a single column, remove any proprietary fields the old platform added, and confirm that dates follow the formats Mailchimp expects.
Mailchimp also offers direct integrations with dozens of third-party tools, including CRMs, e-commerce platforms, and form builders. If your contacts live in one of these tools, connecting it to Mailchimp through the Integrations directory can sync contacts automatically without needing a file at all. This is especially useful for ongoing syncing rather than one-time imports.