Does Sigmera connect to my Mailchimp account?

No. There is no connected app, no OAuth grant, and no API access. Sigmera cleans the exported CSV in your browser, and you import it yourself through Mailchimp's own import tool. Nothing about your audience is exposed, because nothing about your account is reachable from Sigmera in the first place.

Doesn't Mailchimp already remove duplicates for me?

Within one audience, yes — if an email address appears in an import file twice, Mailchimp adds it once. Two limits make cleaning the file worthwhile anyway. Mailchimp does not deduplicate across audiences, so the same person in two audiences counts as two billed contacts, and its match is on the exact address, so casing and stray whitespace across stacked exports can hide duplicates it will not catch.

What file format does Mailchimp need for an import?

A CSV (comma-separated values) or a tab-delimited TXT file. Mailchimp's import tool does not accept .xlsx or .xls, so an Excel workbook has to be converted to CSV first. Clearly label each column so you can map it to an audience field during import; the column holding email addresses is matched to Email Address automatically.

What phone number format does Mailchimp SMS Marketing expect?

E.164 format: a leading + sign, a one-to-three-digit country code, then the subscriber number including area code, up to twelve digits. The SMS phone number field is required for SMS contacts and is separate from the ordinary phone field. Mailchimp also asks you to confirm the contacts gave explicit SMS consent before you import them as subscribed.

What happens to blank cells when I update existing contacts?

They erase data. Mailchimp's import tool warns that when you tick Update any existing contacts, blank fields overwrite and erase the existing value on that contact. So an update file should carry only the columns you mean to change, with no empty cells in them — which is easier to guarantee after you have cleaned and checked the file rather than before.

How should the address field be formatted for import?

Mailchimp asks you to separate each part of the address with two spaces instead of commas, keep each line under 45 characters, and use the two-letter country code rather than the country name. Standardising an address column to that shape with find and replace before import stops Mailchimp rejecting or mangling the field.

Clean CSVs for Mailchimp imports

Mailchimp imports fall over on small things: a phone number with no country code, a name column that should have been two, the same person spread across three exported segments. Sigmera is not a Mailchimp connector and asks for no OAuth grant — you export the CSV, clean it in a browser tab, and add it back through Mailchimp's own import tool. The list of subscribers and their details never leaves your device on the way through.

How it works

1
Export from Mailchimp, or start from the file you were sent
In Mailchimp, click Audience, then Export audience, then Export CSV — only Owners and Admins can do this, and the export is available for 30 days. You may get a ZIP holding separate CSVs for subscribed, unsubscribed, non-subscribed, and cleaned contacts. Or just start from whatever CSV landed in your inbox. Nothing needs to be connected: Sigmera has no Mailchimp integration, no connected app, and no API access to your account.
2
Clean it in a browser tab
Drop the CSV into Sigmera. It is parsed by JavaScript running on your own machine, so a file full of named subscribers and their details is not transmitted anywhere. Deduplicate across your stacked exports, format the phone column to E.164, split names into FNAME and LNAME, and fix the email column — previewing every change before you commit to it.
3
Save a CSV or tab-delimited TXT
Mailchimp's import tool reads a CSV or a tab-delimited TXT file, not an Excel workbook. Sigmera writes a plain UTF-8 CSV by default, so accented names arrive intact and the file is in a format the import tool accepts before you ever open it.
4
Import through Mailchimp's own import tool
In Mailchimp, open Audience, then Add contacts, then Import contacts, and upload your cleaned file. Match each column to an audience field — the email column matches Email Address automatically — and choose a subscriber status. Tick Update any existing contacts only when your update columns are filled, because blank fields overwrite existing data.

Common Mailchimp clean-ups

Deduplicate a list built from several exported segments

Mailchimp deduplicates by email address inside a single audience — import the same address twice in one file and it is added once. What it does not do is dedupe across audiences: the same person in two audiences is billed as two contacts. So the duplicates that survive come from combining exports — a subscribed CSV, an unsubscribed CSV, and a segment download stacked into one file, where casing and stray whitespace stop Mailchimp seeing two rows as the same address. Collapse them before the file goes back in.

Stack your exported CSVs and open them in the remove-duplicates tool
Match on the email column, ignoring case and surrounding spaces
Review the flagged rows and keep the copy with the status you want
Download the deduplicated CSV and import it

Format phone numbers to E.164 for an SMS audience

Mailchimp's SMS Marketing needs every number in E.164 format: a leading +, a one-to-three-digit country code, then the subscriber number up to twelve digits. A column mixing (415) 555-0100, 415.555.0100, and 020 7123 4567 will not import as SMS contacts. The SMS phone field is separate from the ordinary phone field, so the numbers you send texts to have to be clean before the file reaches the import tool.

Load the CSV and select the phone column
Set the default country for numbers that arrive with no code
Rewrite the column to +country-code E.164 form
Check the rows that could not be parsed, then download and import

Split a full-name column into merge fields

Mailchimp stores names in separate audience fields — FNAME and LNAME are the default merge tags used in *|FNAME|* greetings. Most exports from forms, event platforms, and purchased lists hand you a single Full Name column. Import it as-is and the whole name lands in one field, so a *|FNAME|* merge tag renders the entire name and personalisation reads wrong.

Split the name column into first and last, with an optional middle name
Scan the compound surnames and any inverted "Last, First" rows
Map the resulting columns to Mailchimp's FNAME and LNAME fields on import

Clean the email column Mailchimp matches on

Email address is the required field and the identifier Mailchimp uses to decide whether a row updates an existing contact or creates a new one. A leading space in " [email protected]" is a different string, malformed addresses import as contacts you can never email, and — this is the sharp edge — when you tick Update any existing contacts, a blank cell overwrites and erases the data already on that contact. Clean and complete the column first.

Trim whitespace and lowercase the email column
Flag malformed addresses and obvious typos
Remove rows with no usable address so they do not import as dead contacts
Confirm no update columns are blank, then import

Turn an Excel workbook into a CSV Mailchimp will accept

Mailchimp's import tool takes a CSV or a tab-delimited TXT file — it does not accept .xlsx or .xls. A workbook straight out of Excel is rejected before you reach the column-matching step. Flatten the sheet you want to a single CSV, standardise inconsistent values while you are there, and the import goes through on the first try.

Convert the workbook to a single-sheet CSV
Standardise inconsistent values with find and replace
Save the CSV and import it through Mailchimp

Sources

Frequently asked questions

Does Sigmera connect to my Mailchimp account?: No. There is no connected app, no OAuth grant, and no API access. Sigmera cleans the exported CSV in your browser, and you import it yourself through Mailchimp's own import tool. Nothing about your audience is exposed, because nothing about your account is reachable from Sigmera in the first place.
Doesn't Mailchimp already remove duplicates for me?: Within one audience, yes — if an email address appears in an import file twice, Mailchimp adds it once. Two limits make cleaning the file worthwhile anyway. Mailchimp does not deduplicate across audiences, so the same person in two audiences counts as two billed contacts, and its match is on the exact address, so casing and stray whitespace across stacked exports can hide duplicates it will not catch.
What file format does Mailchimp need for an import?: A CSV (comma-separated values) or a tab-delimited TXT file. Mailchimp's import tool does not accept .xlsx or .xls, so an Excel workbook has to be converted to CSV first. Clearly label each column so you can map it to an audience field during import; the column holding email addresses is matched to Email Address automatically.
What phone number format does Mailchimp SMS Marketing expect?: E.164 format: a leading + sign, a one-to-three-digit country code, then the subscriber number including area code, up to twelve digits. The SMS phone number field is required for SMS contacts and is separate from the ordinary phone field. Mailchimp also asks you to confirm the contacts gave explicit SMS consent before you import them as subscribed.
What happens to blank cells when I update existing contacts?: They erase data. Mailchimp's import tool warns that when you tick Update any existing contacts, blank fields overwrite and erase the existing value on that contact. So an update file should carry only the columns you mean to change, with no empty cells in them — which is easier to guarantee after you have cleaned and checked the file rather than before.
How should the address field be formatted for import?: Mailchimp asks you to separate each part of the address with two spaces instead of commas, keep each line under 45 characters, and use the two-letter country code rather than the country name. Standardising an address column to that shape with find and replace before import stops Mailchimp rejecting or mangling the field.