From Postmark to Postal, and what has no match

Add the domain in the dashboard (or with POST /domains), create the records Postal shows in your DNS and ask for verification. Postal signs with DKIM on the postal selector and uses a postal subdomain for the Return-Path, so check that none of your records already uses those names and keep Postmark's until the cutover is done.

• The server token, which only sends, corresponds to a send-only key. Anyone who also manages templates, suppressions and webhooks through the API needs a full-access key.
• The key can be restricted to one domain, which helps separate systems. The full token appears only once, at creation.
• Region: Postal sends from São Paulo by default and lets you choose us-east-1, us-east-2, eu-west-1 or ap-northeast-1 on each domain.

The fields change names and the key changes header. How you tell whether it worked changes too: Postmark responds with ErrorCode in the body, and Postal uses the HTTP status and an error with statusCode, name and message. The success response is just {"id": "…"}. With the Idempotency-Key header, repeating a request does not duplicate the send.

- curl "https://api.postmarkapp.com/email" \-   -X POST \-   -H "Accept: application/json" \-   -H "Content-Type: application/json" \-   -H "X-Postmark-Server-Token: $POSTMARK_SERVER_TOKEN" \-   -d '{-     "From": "[email protected]",-     "To": "[email protected]",-     "Subject": "Your order #10482 is out for delivery",-     "HtmlBody": "<p>Order <b>#10482</b> is on its way.</p>",-     "Tag": "shipping",-     "MessageStream": "outbound"-   }'+ curl -X POST https://api.postal.so/emails \+   -H "Authorization: Bearer $POSTAL_API_KEY" \+   -H "Content-Type: application/json" \+   -d '{+     "from": "Aurora Cosméticos <[email protected]>",+     "to": ["[email protected]"],+     "subject": "Your order #10482 is out for delivery",+     "html": "<p>Order <b>#10482</b> is on its way.</p>",+     "tags": [{"name": "stream", "value": "transactional"}]+   }'

- const response = await fetch('https://api.postmarkapp.com/email', {-   method: 'POST',-   headers: {-     Accept: 'application/json',-     'Content-Type': 'application/json',-     'X-Postmark-Server-Token': process.env.POSTMARK_SERVER_TOKEN,-   },-   body: JSON.stringify({-     From: '[email protected]',-     To: '[email protected]',-     Subject: 'Your order #10482 is out for delivery',-     HtmlBody: '<p>Order <b>#10482</b> is on its way.</p>',-     MessageStream: 'outbound',-   }),- });- const { MessageID, ErrorCode } = await response.json();+ const response = await fetch('https://api.postal.so/emails', {+   method: 'POST',+   headers: {+     Authorization: `Bearer ${process.env.POSTAL_API_KEY}`,+     'Content-Type': 'application/json',+     'Idempotency-Key': 'order-10482-shipped',+   },+   body: JSON.stringify({+     from: 'Aurora Cosméticos <[email protected]>',+     to: ['[email protected]'],+     subject: 'Your order #10482 is out for delivery',+     html: '<p>Order <b>#10482</b> is on its way.</p>',+     tags: [{ name: 'stream', value: 'transactional' }],+   }),+ });+ if (!response.ok) { /* HTTP status and body { statusCode, name, message } */ }+ const { id } = await response.json();

Postmark templates accept blocks and repetitions, like {{#each person}}, and the model (TemplateModel) is an object that can have other objects inside. Postal's only substitute variables, in the {{{NOME}}} format, with three braces, and each value must be text or a number. When your template depends on blocks, move the logic into code: pick between templates or build the HTML yourself and send it in html.

• In Postal you edit a draft and publish; sends always use the latest published version, and old versions can be restored.
• Postal also has layouts, to reuse email designs. Do not treat them as identical to Postmark's layouts: recreate and test.
• In the HTML, values are escaped. A variable with no value and no default value (fallback_value) returns a 422 error.

- <p>Hello, {{name}}!</p>- <p>Your order: {{order.id}}</p>+ <p>Hello, {{{NAME}}}!</p>+ <p>Your order: {{{ORDER}}}</p>

- "TemplateAlias": "order-shipped",- "TemplateModel": { "name": "Ana", "order": { "id": 10482 } }+ "template": {+   "id": "order-shipped",+   "variables": { "NAME": "Ana", "ORDER": "10482" }+ }

In Postmark, a server has streams: transactional (by default, outbound), broadcasts and inbound, up to 10 in total, and suppressions are stored per stream. Postal has no such object. The three uses each have a path, but none of them is a field on the send, and separate suppressions do not exist: the list is single for the team.

• To isolate reputation, use different domains or subdomains (one for transactional, another for campaigns) and a key restricted to each domain.
• The pause for a high bounce or complaint rate applies to the whole team, not to a domain or a tag. See the reputation limits in Limits.
• If your use depends on separate streams with independent suppressions, talk to us before migrating.

If any system sends over SMTP, change the server, user and password and remove the X-PM-* headers. Messages go through the same rules as the API (verified domain, quotas, suppression list) and show up in Emails and Logs.

- host: 'smtp.postmarkapp.com',- port: 587,- secure: false,- auth: { user: process.env.POSTMARK_SERVER_TOKEN, pass: process.env.POSTMARK_SERVER_TOKEN },+ host: 'smtp.postal.so',+ port: 465,+ secure: true,+ auth: { user: 'postal', pass: process.env.POSTAL_API_KEY },

Create the endpoint in Postal (POST /webhooks, with an HTTPS URL and the list of events) and save the signing_secret. The big change is security: Postmark does not sign deliveries, and Postal signs every one. Compute the signature over the body exactly as it arrived, without parsing and rewriting the JSON.

• The webhook-id is the same on every attempt: store the ones you have processed to discard duplicates.
• Respond 2xx right away and process later, in a queue.
• To test without really sending, send emails to the test addresses or use "Send test event" in the dashboard.

- if (req.body.RecordType === 'Bounce') {-   // req.body.Email, req.body.MessageID- }+ const event = verifyWebhook(req.body, req.headers, process.env.POSTAL_WEBHOOK_SECRET);+ if (event.type === 'email.bounced') {+   // event.data.to, event.data.email_id+ }

{
  "type": "email.bounced",
  "created_at": "2026-10-24T13:02:15.004Z",
  "data": {
    "email_id": "019a1b2c-4d5e-7f60-8a9b-0c1d2e3f4a5b",
    "to": ["[email protected]"],
    "subject": "Your order #10482 is out for delivery",
    "tags": { "stream": "transactional" },
    "bounce": {
      "type": "Permanent",
      "subType": "General",
      "message": "smtp; 550 5.1.1 user unknown"
    }
  }
}

Do this before the first real send, so you do not write to people who already opted out or repeat bounces. Postal pauses the team's sending if permanent bounces go over the limit of the account reputation level (3% for a new account) or complaints go over 0.3%; that is why a clean list matters. The example reads the list of one Postmark stream and sends it to Postal in blocks of 100. Repeat for each stream and use a full-access key.

- const base = 'https://api.postmarkapp.com/message-streams';- const dump = await fetch(`${base}/${stream}/suppressions/dump`, {-   headers: {-     Accept: 'application/json',-     'X-Postmark-Server-Token': process.env.POSTMARK_SERVER_TOKEN,-   },- }).then((r) => r.json());- const emails = dump.Suppressions.map((s) => s.EmailAddress);+ for (let i = 0; i < emails.length; i += 100) {+   await fetch('https://api.postal.so/suppressions/batch/add', {+     method: 'POST',+     headers: {+       Authorization: `Bearer ${process.env.POSTAL_API_KEY}`,+       'Content-Type': 'application/json',+     },+     body: JSON.stringify({ emails: emails.slice(i, i + 100) }),+   });+ }

The IDs are different: the MessageID of a Postmark email does not exist in Postal. During the switch, record which provider each email came from and keep receiving Postmark webhooks for what went out through it. Send each flow through a single provider, so you don't duplicate sends or pause everything because of wrong emails.