Migrate from Resend to Unitpost

Before you start

• A Resend API key with full_access. A sending_access key can only send, so the importer cannot read your account with it.
• A Unitpost API key with emails:send for your app, created in API keys.
• A second Unitpost key for the migration steps, with suppressions:write, templates:write, topics: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, to add the new DKIM, MX and SPF records.
• Node.js 18 or later if you run the scripts below; they use the built-in fetch.

The cut-over plan

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

1. 1

   Copy Resend's suppression list

   Do this before anything sends from Unitpost. Page through Resend's GET /suppressions and add the addresses with POST /api/v1/suppressions, up to 1,000 per call. Bounce and complaint rows then block every send here, and running this before the import makes those contacts arrive unsubscribed.

   copy-suppressions.mjs

   import { Unitpost } from "unitpost";
   
   const unitpost = new Unitpost(process.env.UNITPOST_MIGRATION_KEY);
   const resendHeaders = { Authorization: "Bearer " + process.env.RESEND_API_KEY };
   
   // 1. Read Resend's suppression list (100 per page, cursor in "after").
   const emails = [];
   let after = null;
   do {
     const url = "https://api.resend.com/suppressions?limit=100" + (after ? "&after=" + after : "");
     const page = await fetch(url, { headers: resendHeaders }).then((r) => r.json());
     for (const s of page.data) emails.push(s.email);
     after = page.has_more ? page.data[page.data.length - 1].id : null;
   } while (after);
   
   // 2. Add them to Unitpost, up to 1,000 per call. reason "import" also makes
   //    the Migration Assistant import those contacts unsubscribed.
   for (let i = 0; i < emails.length; i += 1000) {
     const { error } = await unitpost.suppressions.create({
       emails: emails.slice(i, i + 1000),
       reason: "import",
     });
     if (error) throw new Error(error.message);
   }

   Run it again on cut-over day to catch addresses Resend suppressed in the meantime.

2. 2

   Run the Migration Assistant

   Paste the key in Settings → Migration. The preview shows counts, samples and conflicts with data you already have; nothing is written until you accept, and you can exclude single items first.

3. 3

   Copy topic opt-outs

   Resend returns a contact's topic choices only one contact at a time (GET /contacts/{id}/topics), and the importer does not call it. For each opt_in topic, collect who opted out and opt them out here with POST /api/v1/email/topics/{id}/opt-out (emails, up to 1,000 per call).

4. 4

   Verify your domains next to Resend

   Open Domains and publish the records shown: MX and SPF on unitpost.<your domain> and a DKIM TXT under _domainkey. Resend's return path lives on the send subdomain, so nothing collides and both stay verified. Keep the one _dmarc record you have, then run POST /api/v1/email/domains/{id}/verify.

5. 5

   Fix variables and publish templates

   Rewrite {{{PRICE}}} as {{PRICE}} (names match exactly), and the reserved {{{FIRST_NAME}}}, {{{LAST_NAME}}}, {{{EMAIL}}} and {{{UNSUBSCRIBE_URL}}} as {{first_name}}, {{last_name}}, {{email}} and {{unsubscribe_url}}. Imports land in the marketing category, which adds an unsubscribe footer; set receipts and resets to transactional and publish with PATCH /api/v1/email/templates/{id}.

   POST /api/v1/email/templates/{id}/render lists missing_variables without sending anything.

6. 6

   Switch the SDK

   The body keeps Resend's field names. What changes is the package, the key, and the path: POST /api/v1/email (singular) instead of /emails. Idempotency-Key works the same way, 24 hours and up to 256 characters.

   send.ts

   // Before: Resend
   import { Resend } from "resend";
   const resend = new Resend(process.env.RESEND_API_KEY);
   const { data, error } = await resend.emails.send({
     from: "Acme <hi@acme.com>",
     to: ["user@example.com"],
     subject: "Your receipt",
     html: receiptHtml,
   });
   
   // After: Unitpost
   import { Unitpost } from "unitpost";
   const unitpost = new Unitpost(process.env.UNITPOST_API_KEY);
   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

   Both products sign with the svix headers (svix-id, svix-timestamp, svix-signature), so your verifier stays. The importer's secret is never shown: rotate it in Webhooks or with POST /api/v1/webhooks/{id}/rotate-secret, deploy it, then set status to enabled. A switched-off endpoint does not queue events.

8. 8

   Send tests

   Send one of each template with POST /api/v1/email/templates/{id}/test-send, and fire POST /api/v1/webhooks/{id}/test at each endpoint to prove the new secret verifies.

9. 9

   Move traffic in stages

   Route one message type through Unitpost first and watch email.bounced and email.complained for it, then move the rest. Both providers stay verified on the domain, so going back is a config change.

10. 10

    Cancel Resend last

    Close the account only after its scheduled emails have gone out, its webhooks have gone quiet, and the checks below are done.

Before you cancel Resend

• Re-run the suppression copy from step 1 so addresses Resend suppressed during the overlap are blocked here too.
• Let scheduled emails and broadcasts at Resend finish or cancel them; scheduled sends do not move.
• Export the logs and broadcast stats you want to keep; Resend's pricing page lists 30-day data retention, and none of it moves.
• Delete Resend's DKIM record and the MX and SPF records on its send subdomain once no mail goes through Resend. Keep _dmarc and Unitpost's records.
• Revoke Resend API keys and delete its webhook endpoints so nothing keeps sending or posting.

Facts about Resend checked 2026-11-02. Providers change their APIs and plans; check their docs before you rely on a detail.