C

MAIL MAX

Mailing List Converter

OFFLINE · GDPR-SAFE

V 1.0.0

Studio

zigmoon.com

Author

Simon Dupont-Gellert

Supports

19 newsletter providers

Mailchimp · Brevo · HubSpot…

Drop your CSV files here

One or many · auto-merge · auto-dedupe

— or —

Ready to export

0 emails· Mailchimp format · mailchimp-list.csv

Preview · Mailchimp format

0 rows · 0 dropped · 0 duplicates removed

Drop a CSV to see the preview

MAIL MAX · The king of mailing list CSVs

Convert any CSV mailing list to 19 newsletter providers — free, offline, GDPR-safe

MAIL MAX is a free in-browser tool that takes any messy CSV — exported from Excel, Google Sheets, Shopify, WooCommerce, an old Mailchimp account, or scraped together from several years of signups — and re-emits it in the exact import format expected by Mailchimp, Brevo, HubSpot, MailerLite, Klaviyo, Beehiiv, Substack, ConvertKit (Kit), ActiveCampaign and 10 other major email service providers. Files are read locally in your browser; nothing is uploaded, nothing is logged, nothing leaves your device.

19 supported newsletter providers

MailchimpBrevo (Sendinblue)MailjetMailerLiteHubSpotActiveCampaignConvertKit (Kit)KlaviyoBeehiivSubstackGetResponseAWeberConstant ContactOmnisendSendGridLoopsResendCampaign MonitorDrip

What MAIL MAX actually does

1 · Reads any CSV dialect

Auto-detects comma, semicolon, tab and pipe delimiters. Handles quoted fields, embedded newlines and BOM markers per RFC 4180. European Excel exports? No problem.

2 · Maps headers intelligently

Recognises 60+ header aliases in English, French, Spanish and German — email, e-mail, courriel, correo, FIRSTNAME, prénom, Nom, téléphone, etc. If the email column has no header, a heuristic finds it.

3 · Merges & deduplicates

Drop multiple files at once — they are combined and deduplicated by lowercased email. Invalid addresses are filtered out. Optional UTF-8 BOM keeps accents readable in Excel.

4 · Re-emits the right schema

Outputs each provider's exact column order: Email Address for Mailchimp, EMAIL/FIRSTNAME for Brevo, email/firstname for Mailjet, and so on. Drop into the destination ESP — it imports without errors.

5 · 100% offline & GDPR-safe

Every byte is processed in your browser. No API call, no server, no upload. You can verify it in DevTools → Network. Perfect for client lists, B2B leads and any data subject to GDPR.

6 · Installable as an app

Progressive Web App with offline-first service worker. Installs on Windows, macOS, Linux, Android and iOS. Opens .csv files via the OS file handler.

Common migrations MAIL MAX handles in 30 seconds

Mailchimp → Brevo. Old free Mailchimp account hitting the 500-contact wall? Export, drop, pick Brevo, import. Done.

Mailchimp → MailerLite. Switching for better automation? Same workflow, MailerLite-ready file in seconds.

Substack → Beehiiv. Newsletter writers migrating for monetisation features. Substack export is just emails — Beehiiv accepts it directly.

ConvertKit → Kit (Klaviyo / Beehiiv). Now that ConvertKit became Kit, exports still need cleaning. We handle both naming conventions.

Klaviyo → HubSpot. Moving e-commerce list into a CRM. We map phone, region, zip and country to HubSpot's expected columns.

Shopify export → any ESP. Shopify customer exports have non-standard headers. MAIL MAX maps them automatically.

Why use MAIL MAX instead of Excel or an online converter?

Capability	Excel / Sheets	Online CSV converter	MAIL MAX
Knows each ESP's exact column schema	No	Rarely	19 providers
Auto-maps multilingual headers	Manual	No	EN/FR/ES/DE
Cross-file deduplication by email	Macros required	Limited	Built-in
Drops invalid addresses	Manual	Sometimes	Automatic
UTF-8 BOM for Excel re-open	No	No	One click
Files never uploaded (GDPR)	Local	Uploaded	Local
Time to clean a 5K-contact list	20–40 min	3–5 min + risk	~30 sec
Cost	License	Often paid	100 free credits, then €5/1k — €300/100k

Frequently asked questions

Is my contact list uploaded to a server?

No. MAIL MAX runs 100% in your browser. There is no API call, no server, no upload. You can verify it by opening browser DevTools → Network tab and watching for zero outgoing requests during conversion. This is what makes it GDPR-safe by design.

Which email service providers are supported?

19 providers as of April 2026: Mailchimp, Brevo (ex-Sendinblue), Mailjet, MailerLite, HubSpot, ActiveCampaign, ConvertKit (Kit), Klaviyo, Beehiiv, Substack, GetResponse, AWeber, Constant Contact, Omnisend, SendGrid, Loops, Resend, Campaign Monitor, and Drip.

How much does MAIL MAX cost?

100 email credits are free on first launch — 1 credit = 1 exported email. Beyond that, top up with one-shot PayPal packs: 1 000 emails — €5, 10 000 emails — €50, or 100 000 emails — €300 (€0.003/email, -40% volume discount). No subscription, no signup, credits never expire.

How do I convert a Mailchimp CSV to Brevo format?

Open the app, drop your Mailchimp export into the dropzone, click "Brevo (ex-Sendinblue)" in the sidebar, then click Download CSV. The file imports directly into Brevo's contact import without any column mapping needed.

Can I merge multiple CSV files?

Yes. Drop as many files as you want. They are merged and deduplicated by lowercased email address. The preview shows you exactly how many duplicates and invalid emails were removed.

Does it work with semicolon-separated CSVs from European Excel?

Yes. The delimiter is auto-detected from comma, semicolon, tab and pipe. Quoted fields and embedded newlines are handled correctly per RFC 4180.

Does it preserve accented characters (é, ñ, ü, etc.)?

Yes. Files are read as UTF-8. Enable the "Add UTF-8 BOM" option if you plan to open the export in Excel — it forces Excel to read it as UTF-8 instead of mojibake.

Does it remove invalid email addresses?

Yes, when the "Drop invalid emails" option is enabled (on by default). Entries that don't match the standard email pattern are filtered out before export, protecting your sender reputation.

Can I install it as a desktop or mobile app?

Yes. Click the install icon in the header, or use your browser's "Install app" / "Add to Home Screen" menu. It works on Windows, macOS, Linux, Android and iOS, and runs offline after the first visit.

Is MAIL MAX GDPR-compliant?

Yes. Because all processing happens in your browser with zero network traffic, no personal data is ever transmitted, stored or shared. There is no third-party data controller relationship to worry about — the data stays on your device.

Does it work without internet?

Yes. After the first visit, the service worker caches the entire app. You can disconnect and keep using it. PayPal checkout is the only feature that requires internet.

Do credits expire?

No. Credits are stored locally in your browser and never expire. Top up once, use forever — no subscription, no recurring charges.

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