Migrate from Postmark to Unitpost

Before you start

• An Account API token (Account → API Tokens). It reads domains and, through each server's own token, every server's templates, suppressions and webhooks. A server token reads one server and no domains.
• A list of which message streams are broadcast streams, for step 2.
• A Unitpost API key with emails:send for your app, created in API keys.
• A second Unitpost key for the migration steps, with contacts:write, domains:write, suppressions: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.

The cut-over plan

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

1. 1

   Run the Migration Assistant

   Paste the token in Settings → Migration. The preview lists suppressions with their Postmark reason (bounce, complaint, manual). Stop before you accept if you have broadcast streams.

2. 2

   Keep broadcast unsubscribes off receipts

   Postmark scopes a suppression to one stream; here it covers the workspace and every send. Pull each broadcast stream's list with GET /message-streams/{stream_id}/suppressions/dump, exclude its ManualSuppression addresses in the preview, then import them as unsubscribed contacts (POST /api/v1/contacts/imports with unsubscribed: true). An unsubscribed contact gets no marketing but still gets receipts and resets.

   Already accepted? Remove those rows with DELETE /api/v1/suppressions/{email} first, then import the contacts.

3. 3

   Verify your domains next to Postmark

   Open Domains and publish the records shown: MX and SPF on unitpost.<your domain> and a DKIM TXT under _domainkey. Postmark's return path stays on its own CNAME (pm-bounces by default), so both stay verified. Unitpost has no single-address verification: an address from a sender signature needs its domain verified here.

4. 4

   Merge layouts and publish templates

   Paste each layout's wrapper around the template body it served, and delete the imported layout drafts. Plain {{name}} placeholders work; Mustachio sections ({{#...}}) do not, because Unitpost templates have no loops or conditionals. Postmark mail is usually transactional, so set category to transactional (imports land as marketing, which adds an unsubscribe footer) and publish with PATCH /api/v1/email/templates/{id}.

5. 5

   Switch the client

   Fields move from PascalCase to snake_case (HtmlBody becomes html), TemplateModel becomes template.variables, and the stream disappears: the template's category does that job. first_name, last_name and email are reserved variable names here.

   send.ts

   // Before: Postmark
   import { ServerClient } from "postmark";
   const postmark = new ServerClient(process.env.POSTMARK_SERVER_TOKEN);
   await postmark.sendEmailWithTemplate({
     From: "hi@acme.com",
     To: "user@example.com",
     TemplateAlias: "password-reset",
     TemplateModel: { reset_url: resetUrl },
     MessageStream: "outbound",
   });
   
   // 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",
     template: { id: "tmpl_123", variables: { reset_url: resetUrl } },
   });

6. 6

   Add signature checks to webhook receivers

   Postmark protects webhooks with HTTP auth or headers you set; Unitpost signs each delivery with a whsec_ secret in the svix format (svix-id, svix-timestamp, svix-signature). Rotate the secret in Webhooks to see it, verify with the SDK's verifyWebhook, then set status to enabled. A switched-off endpoint does not queue events.

7. 7

   Move inbound mail

   If you use an inbound stream, turn receiving on for the verified domain (PATCH /api/v1/email/domains/{id} with capabilities.receiving set to enabled), subscribe an endpoint to email.received, then switch the MX record.

8. 8

   Send tests

   Send each template once with POST /api/v1/email/templates/{id}/test-send and fire POST /api/v1/webhooks/{id}/test at each endpoint.

9. 9

   Move traffic in stages

   Move the mail where a delay costs least first, and password resets and sign-in codes last, watching email.bounced and email.delivery_delayed as you go. Postmark stays verified, so rolling back is a config change.

10. 10

    Cancel Postmark last

    Finish the checks below, then delete the servers and close the account.

Before you cancel Postmark

• Export the message history you need; Postmark keeps it 45 days by default and none of it moves.
• Pull each stream's suppression dump one last time and add new hard bounces and complaints here.
• Delete Postmark's DKIM record and its return-path CNAME once no mail goes through Postmark. Keep _dmarc and Unitpost's records.
• Move the MX record off Postmark's inbound address if you used an inbound stream.
• Revoke server and account tokens and delete webhooks on every server.

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