Postmark Email Tester — Test API & SMTP Sending

Send Method

Send via HTTP POST to api.postmarkapp.com/email. Best for modern apps.

Authentication

Server API Token

Found in Postmark → Server → API Tokens. Use POSTMARK_API_TEST for dry-run.

Sender

From address

Must be a confirmed Sender Signature in Postmark.

Recipient

Safe test sink: test@blackhole.postmarkapp.com

Message

Subject HTML Body Preview email ↗

Connection issue? Make sure this app is hosted on a PHP server. Use Copy as cURL to test from terminal without a server.

FAQ

Where do I find my Server API Token?

Log in to Postmark → select your Server → click the API Tokens tab. Copy the Server API token shown there. Each server has its own unique token.

Verified email vs verified domain?

Verified Email: You confirm a single address (Sender Signature). You can only send from that exact address.
Verified Domain: You verify your entire domain via DNS (DKIM + Return-Path). Once verified, you can send from any address @yourdomain.com.

How do I verify a domain?

Go to Sender Signatures → Add Domain → enter your domain. Postmark gives you DNS records (DKIM and Return-Path) to add at your DNS provider. Once propagated and confirmed, the domain is verified.

Why does Send fail with a network error?

Postmark blocks browser-side API calls (CORS) to protect your token. Use Copy as cURL and paste in your terminal. For production, always call Postmark from your server/backend.

What is POSTMARK_API_TEST?

A special token for dry-run testing. Postmark validates your payload and returns success without delivering the email. Great for checking your request format.

API vs SMTP — which should I use?

	REST API	SMTP
Speed	Fastest — HTTP POST	Slower — SMTP handshake
Auth	X-Postmark-Server-Token header	Username & password = token
Features	Full (templates, tags, streams, batch)	Basic sending + headers
Best for	Modern apps, serverless	Legacy, CMS, WordPress
Endpoint	`api.postmarkapp.com/email`	`smtp.postmarkapp.com:587`
Batch	Up to 500/call	1 per connection

Is my API token safe here?

Yes. Everything runs in your browser. Token is only sent to api.postmarkapp.com over HTTPS (or stays local in cURL). No backend, no cookies, no storage. Wiped on tab close.

What's test@blackhole.postmarkapp.com?

A safe sink address from Postmark. Emails are accepted (you get a Message ID) but never delivered to any inbox. Perfect for testing.