Migrate from Mailchimp to Unitpost

Before you start

• A Mailchimp API key: Profile → Extras → API keys → Create A Key. An Owner, Admin or Manager can create one.
• Mailchimp keys always have full access to the account; there is no read-only key. The importer only reads, and the last step revokes the key.
• A Unitpost API key for your app with emails:send, plus contacts:write and segments:write if your signup form adds contacts, created in API keys.
• A second Unitpost key for the migration steps, with contacts:write, templates:write and webhooks:manage, saved as UNITPOST_MIGRATION_KEY. Keep it out of your app and revoke it once the move is done.
• Access to your DNS host.
• If you text contacts: SMS on Unitpost is on paid plans only, and marketing texts need consent on record per contact.

The cut-over plan

Mailchimp keeps sending until the last step, so there is no gap in delivery.

1. 1

   Run the Migration Assistant

   Paste the key in Settings → Migration. The preview counts what it found and lists what it leaves out: pending contacts, saved templates it can't read, advanced segments and your automations. Suppressions are written before contacts, so cleaned and complained addresses land unsubscribed.

2. 2

   Verify your domains next to Mailchimp

   Open Domains and publish the records shown: MX and SPF on unitpost.<your domain> and a DKIM TXT under _domainkey. They sit beside Mailchimp's DKIM records, so both stay authenticated while you move. Keep your single _dmarc record.

3. 3

   Review merge tags and publish

   Exact merge tags are already rewritten: *|FNAME|* is {{first_name}}, *|LNAME|* is {{last_name}}, *|EMAIL|* is {{email}}, *|UNSUB|* is {{unsubscribe_url}}, and your own merge fields map by tag. Unitpost fills flat {{name}} placeholders only, with no conditionals, so rewrite *|IF:…|* blocks, *|LIST:ADDRESS|* and *|ARCHIVE|* by hand. Imports land as marketing drafts with Unitpost's unsubscribe footer; publish with PATCH /api/v1/email/templates/{id}.

4. 4

   Rebuild the saved templates you still use

   Mailchimp's API doesn't share saved template HTML, and Mailchimp can't export drag-and-drop templates at all. For a custom-coded template, export its HTML in Mailchimp and paste it into a new template in code mode. Rebuild drag-and-drop ones in the visual editor.

5. 5

   Point signups at Unitpost

   Mailchimp forms and landing pages keep adding people to Mailchimp. Send signups from your own form with POST /api/v1/contacts, then add them to a segment or topic. Mailchimp's status: "subscribed" is the default here. Unitpost has no built-in email double opt-in, so if you used Mailchimp's, confirm the address in your app before you create the contact.

   signup.ts

   // Before: Mailchimp
   await fetch("https://api.mailchimp.com/3.0/lists/" + AUDIENCE_ID + "/members", {
     method: "POST",
     headers: { Authorization: "Bearer " + process.env.MAILCHIMP_API_KEY, "content-type": "application/json" },
     body: JSON.stringify({
       email_address: "user@example.com",
       status: "subscribed",
       merge_fields: { FNAME: "Ada", LNAME: "Lovelace" },
     }),
   });
   
   // After: Unitpost
   import { Unitpost } from "unitpost";
   const unitpost = new Unitpost(process.env.UNITPOST_API_KEY);
   const { error } = await unitpost.contacts.create({
     email: "user@example.com",
     first_name: "Ada",
     last_name: "Lovelace",
   });
   // 409 conflict: the contact already exists, which is fine for a signup.
   if (error && error.code !== "conflict") throw new Error(error.message);
   await unitpost.segments.addMember("seg_123", { contact: "user@example.com" });

6. 6

   Switch transactional sends

   Only if you send through Mailchimp Transactional (formerly Mandrill). messages.send becomes email.send: from_email and from_name become one from string and to takes addresses. For a stored template, merge_vars become template.variables. Over SMTP, change the host and credentials as in the SMTP table. Sends here accept an Idempotency-Key.

   send.ts

   // Before: Mailchimp Transactional
   import mailchimpTransactional from "@mailchimp/mailchimp_transactional";
   const mailchimp = mailchimpTransactional(process.env.MAILCHIMP_TRANSACTIONAL_KEY);
   await mailchimp.messages.send({
     message: {
       from_email: "hi@acme.com",
       from_name: "Acme",
       to: [{ email: "user@example.com", type: "to" }],
       subject: "Your receipt",
       html: receiptHtml,
     },
   });
   
   // After: Unitpost
   const { data, error } = await unitpost.email.send({
     from: "Acme <hi@acme.com>",
     to: "user@example.com",
     subject: "Your receipt",
     html: receiptHtml,
   });

7. 7

   Re-key and enable webhooks

   Mailchimp posts audience events as form fields, signed with X-Mailchimp-Signature when signing is on. Unitpost posts JSON and signs it with a whsec_ secret in svix-id, svix-timestamp and svix-signature. Rotate the secret in Webhooks to see it, update your handler, then set status to enabled.

8. 8

   Check SMS consent before texting

   Numbers whose opt-in had no date arrived without consent. Record consent where the contact gave it (POST /api/v1/contacts/{id}/sms-consent) or ask them to confirm with POST /api/v1/contacts/{id}/sms-opt-in-request. Mailchimp SMS opt-outs came over and stay in force.

9. 9

   Test, move traffic, then revoke the key

   Send each template with POST /api/v1/email/templates/{id}/test-send and fire POST /api/v1/webhooks/{id}/test at each endpoint. Send your next campaign from Unitpost to a small segment first, then to everyone. Then revoke the Mailchimp key under Profile → Extras → API keys.

Before you cancel Mailchimp

• Export each audience as CSV, including archived contacts, which the importer doesn't read.
• Export the campaign reports you want to keep; send history doesn't move.
• Write down what each Customer Journey and classic automation does, with its timing.
• Export the HTML of every custom-coded template you still use.
• Delete Mailchimp's domain authentication records once no mail goes through Mailchimp. Keep _dmarc and Unitpost's records.
• Revoke the Mailchimp API key you used for the import.

Facts about Mailchimp checked 2026-11-05. Providers change their APIs and plans; check their docs before you rely on a detail.