Migration from Postmark

Move transactional sends from Postmark to SuperSend TX without changing your product’s email jobs — receipts, password resets, alerts, and invites still go out over POST /emails.

Why teams switch

HTTP API + npm SDK with a short path from API key to first send
Owned transactional mail infrastructure, not a thin layer on rented cloud email
Sandbox → Pool → Dedicated so you can test free, run production on a paid shared transactional network, then isolate on managed servers and IPs when you need allowlists

Quick mapping

Postmark	SuperSend TX
Server API token	`stx_...` API key (`Authorization: Bearer`)
`https://api.postmarkapp.com`	`https://api.supersendtx.com`
`POST /email`	`POST /emails`
Verified Sender Signature / domain	Verified sending domain in SuperSend TX
Message Streams (Transactional)	Transactional-only product (no cold/marketing mix)
Webhooks	Webhooks + dashboard activity

Minimal send

curl -X POST https://api.supersendtx.com/emails \
  -H "Authorization: Bearer $SUPERSENDTX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "you@yourdomain.com",
    "to": "user@example.com",
    "subject": "Hello",
    "html": "<p>It works.</p>"
  }'

Node:

npm install supersendtx

import { SuperSendTX } from 'supersendtx'

const client = new SuperSendTX(process.env.SUPERSENDTX_API_KEY)
await client.emails.send({
  from: 'you@yourdomain.com',
  to: 'user@example.com',
  subject: 'Hello',
  html: '<p>It works.</p>',
})

Migration checklist

Create a SuperSend TX account and API key
Add and verify your sending domain (Domains)
Point your app’s send client at https://api.supersendtx.com with stx_...
Map Postmark fields: From → from, To → to, Subject → subject, HtmlBody → html, TextBody → text, ReplyTo → reply_to
Reconfigure webhooks to SuperSend TX endpoints (Webhooks)
Send a canary through Sandbox or your verified domain, then cut over

HTTP aliases accepted today: htmlBody / html_body, textBody / text_body / plain_body, replyTo → reply_to. Postmark’s PascalCase HtmlBody is not accepted — map it to html (or htmlBody) in your client. New code should use canonical names (html, text, reply_to).

Domains and DNS

Production from addresses must use a domain verified in SuperSend TX. Cloudflare and GoDaddy apply flows can write records for you — see Domains.