Mailchimp Import File Format: One Email per Contact, the Tags Column and Cleaning the List First

Mailchimp wants one email address per contact in the email column, optional name and phone columns, and a single column labeled Tags for any tags. Get those right, verify the list, and the import goes through without surprises. The rules here come from Mailchimp's format guidelines for your import file, read on 9 November 2026. The verification step is ours, and it matters most when the list is new to you.

Format your Mailchimp file →

The email column

Mailchimp's guidelines say the email address is required for email contacts, with one address per contact. They ask you to check for three things before importing:

1. Missing information. Empty cells, or cells that hold only a name.
2. Unsupported characters. Mailchimp says international characters like ñ or é are supported only after the @ symbol.
3. Extra spaces before or after the address.

Two addresses in one cell, such as "[email protected]; [email protected]", don't fit, so split them into rows. A spreadsheet that has been through several hands usually has all three problems. The email list cleaner and the duplicate email remover take care of the mechanical ones.

Names and phone numbers

• Names: first and last names go in text fields. Mailchimp says text fields hold up to 255 bytes, which is about 255 characters in many alphabets, and emoji and some symbols use more bytes per character. If your export has one Name column, the name splitter separates first and last.
• Phone: the standard phone field uses international format by default, and US-only audiences can choose the (###) ###-#### format in the audience field settings. SMS phone numbers are a separate field and must be E.164: a leading +, a country code of one to three digits, and a subscriber number of up to 12 digits. You can import SMS contacts only from your sending country, according to the page. The phone number formatter writes numbers with the country code.

The same page limits address lines to under 45 characters, asks for two-letter country codes, limits ZIP fields to five digits, and accepts birthdays as MM/DD or DD-MM and dates as YYYY-MM-DD or MM-DD-YYYY. Most imports only need email, names and tags, so we don't go further.

Tags

Tags are how you remember where a contact came from. Mailchimp's rules:

• Use a single column labeled Tags.
• Separate several tags for one contact with commas.
• A tag that contains a comma must be in double quotes, such as "Monday, Wednesday".
• Names can be up to 100 characters; longer names are truncated.
• Emoji can't be imported, so replace them with text.
• Tags that don't exist are created during the import.

That last rule has a side effect: a typo in one row creates a separate tag instead of an error. "Webinar-Nov" and "Webinar-Nov " (with a trailing space) are not the same name to a human reading a tag list. If you use the formatter, the tag you type is written to every row, with emoji and quotes stripped and long names cut to 100 characters and flagged.

A good habit is one tag for the source and one for the date, for example "trade-show" and "2026-11". Six months later you can tell which imports gave you the bounces.

What the file should look like

Column	What goes in it
Email Address	one address per row, lower case, no spaces
First Name	text
Last Name	text
Phone Number	international format
Tags	commas between tags, quotes around a tag with a comma

The page shows a sample CSV and suggests opening it in a spreadsheet program such as Excel or Google Sheets. It doesn't list other accepted file types, and we won't either; the formatter downloads a CSV. In the import, Mailchimp asks you to match each column to a field, so clear column labels save time.

Why verify before you import

A first campaign to a new, unchecked list is where a bad list shows up. Typical sources of dead addresses in a list you're about to import:

• An old newsletter list from another tool, left alone for a year.
• A trade-show or webinar export with hand-typed addresses.
• A purchased or scraped list. Mailchimp may warn about this; see our post on the Omnivore warning.
• A migration from another platform. Moving from Mailchimp to Klaviyo covers the reverse direction and the suppression lists that must go with you.

Verification fixes the first two. It sorts rows into valid, invalid and risky:

• Valid: import.
• Invalid: leave out. These would bounce.
• Risky or unknown: the answer wasn't clear, often a domain that accepts all mail. Import them as a separate tag, such as "risky", and send to that group on its own after a clean first campaign.

If you're also wondering what happens once the list is inside, cleaned contacts in Mailchimp explains the status Mailchimp gives to addresses that bounce. Removing bounces before a campaign and cleaning a Mailchimp list cover the maintenance side, and the Mailchimp bounce rate warning shows what a bad send can lead to.

A routine for each import

1. Collect the export. One row per person.
2. De-duplicate and trim.
3. Verify at /verify, and keep valid rows plus any risky rows you are tagging.
4. Format with the Mailchimp formatter: names split, addresses lower-cased, repeats merged, an optional tag on every row.
5. Import in Mailchimp with Import contacts, upload the file, and match each column to its field.
6. Check the first campaign against the tag for that import, and look at bounces by tag.

Consent comes first

Verification says whether a mailbox exists, not whether the person agreed to receive your mail. The formatter writes no permission columns. Import only people who agreed, and follow the rules that apply where they live.

Try it on your own list

Upload a sample at /verify. The first 100 checks are free with a Google sign-in, no card.

Pro, $39 a month: Unlimited email verification.* Never metered, never cut off. See pricing.

*Fair use: the first 100,000 checks a month at full speed, then slower, never cut off.