Migrate from Postmark

What changes, what doesn't

Both are deliverability-focused, JSON-first transactional APIs with a similar philosophy. A strict separation between transactional and broadcast sending, and no tolerance for spammy behavior. The request shape is close enough that most of this migration is renaming fields. The honest comparison, including where Postmark is the better choice (its delivery visibility is genuinely excellent), is at euromail vs Postmark.

Verify your domain on EuroMail while Postmark still handles production traffic, then cut over.

API mapping

The most consequential difference isn't a field name: EuroMail's idempotency_key prevents duplicate sends server-side, whereas Postmark's approach is client-side (store MessageID, check before retrying). If your integration retries on timeout, this closes a gap you may have been handling manually.

Code before and after

curl:

# Before: Postmark
curl -X POST https://api.postmarkapp.com/email \
  -H "X-Postmark-Server-Token: your-server-token" \
  -H "Content-Type: application/json" \
  -d '{
    "From": "[email protected]",
    "To": "[email protected]",
    "Subject": "Welcome aboard",
    "HtmlBody": "<h1>Welcome!</h1>",
    "MessageStream": "outbound"
  }'

# After: EuroMail
curl -X POST https://api.euromail.dev/v1/emails \
  -H "X-EuroMail-Api-Key: em_live_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "[email protected]",
    "to": "[email protected]",
    "subject": "Welcome aboard",
    "html_body": "<h1>Welcome!</h1>"
  }'

TypeScript:

// Before: Postmark
import { ServerClient } from "postmark";
const client = new ServerClient(process.env.POSTMARK_SERVER_TOKEN!);

await client.sendEmail({
  From: "[email protected]",
  To: "[email protected]",
  Subject: "Welcome aboard",
  HtmlBody: "<h1>Welcome!</h1>",
});

// After: EuroMail
import { EuroMail } from "@euromail/sdk";
const euromail = new EuroMail({ apiKey: process.env.EUROMAIL_API_KEY! });

await euromail.emails.send({
  from: "[email protected]",
  to: "[email protected]",
  subject: "Welcome aboard",
  html_body: "<h1>Welcome!</h1>",
});

Python, Rust, and Go SDKs follow the same field names as the REST API.

SMTP cutover

EuroMail follows the SendGrid/SES convention of a literal apikey username with the key as the password, rather than Postmark's token-as-both-fields pattern. A two-field change in your SMTP config. Full walkthroughs in Send Email via SMTP.

DNS: verify your domain before switching

1. Add your domain in the EuroMail dashboard and publish its DKIM, SPF, and DMARC records. Domain Verification.
2. Keep Postmark's records in place during the dual-run. Different DKIM selectors and stacked SPF include:s let both providers verify at once.
3. Remove Postmark's records after cutover, on your own schedule.

Webhook event mapping

Signature verification changes the most here: Postmark doesn't support HMAC webhook signatures at all. It recommends Basic Auth on the callback URL or IP allowlisting instead. EuroMail signs every payload with HMAC-SHA256 in the X-EuroMail-Signature header, which is a strictly stronger guarantee. You can drop the URL-embedded credentials or IP allowlist and verify the payload itself. See Webhooks.

Bring your suppression list

Export bounces and spam complaints from the Postmark dashboard, then replay them:

curl -X POST https://api.euromail.dev/v1/suppressions \
  -H "X-EuroMail-Api-Key: em_live_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "email_address": "[email protected]",
    "reason": "migrated from Postmark: hard bounce"
  }'

Details in Suppression Lists.

Honest gaps

• Message Streams are structural, not a toggle. Postmark's MessageStream field routes one API to two different sending contexts (transactional vs. broadcast) with independent suppression lists. EuroMail keeps these as genuinely separate systems. /v1/emails for transactional, Newsletters for broadcast, with their own suppression semantics, matching Postmark's isolation but through different endpoints rather than a request field.
• Bounce/spam hooks feeding external tools (e.g. a CRM synced via Postmark's granular bounce types) will need their handler updated for EuroMail's event names. See the mapping table above.
• Full comparison at euromail vs Postmark.

Cutover checklist

1. Create a EuroMail account and an API key with the emails:send scope (API Keys).
2. Verify your sending domain; confirm DKIM/SPF/DMARC show green.
3. Register your webhook endpoint. Add HMAC verification, since Postmark never had it.
4. Import suppressions from your Postmark export.
5. Switch the endpoint, auth header, and PascalCase → snake_case field names (or the SMTP username/password), accepting 202 as success.
6. Send a staging email end-to-end; confirm the delivered webhook arrives.
7. Cut production traffic over; watch the first hour in Analytics and Deliverability Insights.
8. Keep Postmark read-only for a rollback window, then retire it.