How to Migrate an Email List from Mailchimp to Substack
Substack imports a Mailchimp CSV to a subscriber list in about 10 minutes, but only email address and name transfer — tags, segments, automations, open history and e-commerce data stay behind. Plan around that gap before you export, or you’ll rebuild segmentation from memory.
For lists under about 5,000 contacts the free tier can still be a marketing list while you operate the publication, which makes the transition less abrupt.
What actually transfers from Mailchimp?
| Data | Transfers to Substack? | Notes |
|---|---|---|
| Email address | Yes | Primary key, deduplicated |
| First / last name | Yes | If columns are mapped correctly |
| Tags | No | Rebuild as post categories or segments |
| Groups / interests | No | Lost |
| Automation flows | No | Nothing equivalent exists |
| Open and click history | No | Export the CSV for your own records |
| Purchase, e-commerce | No | Never exported |
Substack’s model is simpler than Mailchimp’s by design. It’s a publication platform, not a marketing automation suite. If you run a 6-email onboarding sequence today, it doesn’t exist after the move. That alone changes the plan.
Step 1: Export and clean before you import
In Mailchimp, go to Audience > All contacts > Export Audience, choose the whole audience, and download the CSV. Clean it locally:
- Remove contacts with
unsubscribedorcleanedstatus. - Remove the
Non SubscribedandTransactionalgroups if you have them. - Deduplicate by email, keeping the row with the most recent activity date.
Importing your unsubscribes back into a new platform is the fastest way to earn spam complaints. Substack doesn’t know they opted out of anything.
Step 2: Import in batches, not in one shot
Substack’s import accepts CSV under Settings > Import. Large single files fail more often than batches of 500, and a failed import part-way leaves you unsure what landed. Do 500 at a time and check the subscriber count after each batch.
Map columns explicitly. Substack guesses email and name, and it will quietly drop a column it doesn’t recognise rather than erroring — which looks like a clean import with missing data.
Step 3: Decide about re-consent
This is the part with legal weight. If your Mailchimp list was built with a checkbox that said “Mailchimp newsletters”, you do not have automatic permission to send from Substack under a different brand. In practice most small lists transfer fine under the same business name, but if the publication is a new name on a new domain, send one plain-text note before importing: here’s where I’m moving, click to keep receiving.
Substack can’t send that note to people who aren’t subscribers yet, so use Mailchimp for the announcement. Keep the list in Mailchimp for 30 days to run it.
Step 4: Warm up deliverability
The first Substack send to a transplanted list lands from a new sending domain. Two things matter: send your first post to a small segment first (say your 50 most engaged), then the rest; and make sure the From address and publication name match what people recognise.
Expect 5-10% of an old list to never receive again — stale addresses, corporate filters, people who used the newsletter as a formality. That’s normal and not a sign the migration failed.
Step 5: Rebuild the one automation that matters
You can’t rebuild a six-email onboarding flow. You can rebuild the important half: the welcome email on subscribe plus one follow-up. Put your best archived post in the follow-up. Substack lets you schedule this, and it’s the highest-value item in the whole migration.
Is it worth moving at all?
Yes if your main pain is Mailchimp’s cost scaling with list size while your revenue is from paid subscriptions. Running the numbers: a 10,000-contact Mailchimp list at roughly $100/month against Substack’s 10% of paid revenue — Substack becomes cheaper once you’re doing more than about $1,000/month in paid subs.
No if you depend on segmentation, shopping integrations or behavioural triggers to sell. Substack has no equivalent, and you’ll lose measurable revenue, not just convenience. Teams in that position are better served by an email provider with subscriber pricing and a separate paid-content layer.
Quick Summary
- Mailchimp to Substack import moves email and name only.
- Tags, segments, automations, open history and purchases do not transfer.
- Export, remove unsubscribes and deduplicate before importing.
- Import in 500-row batches and verify the count after each batch.
- Keep Mailchimp live for 30 days to send the migration announcement.
