Postmark SMTP settings: smtp.postmarkapp.com, port 587, server API token
Postmark SMTP: host smtp.postmarkapp.com, ports 25/2525/587 STARTTLS, username and password both set to the Server API Token (or Access/Secret SMTP tokens), plus the X-PM-Message-Stream header for streams. Transactional-only rules.
Postmark outgoing mail server:
smtp.postmarkapp.com, port <code>587</code> (STARTTLS) or <code>2525</code> (STARTTLS) or <code>25</code> (STARTTLS), username = the Server API Token (or the SMTP Access Key), password = the same Server API Token.
Postmark SMTP settings at a glance
| Outgoing (SMTP) host | smtp.postmarkapp.com (broadcasts: smtp-broadcasts.postmarkapp.com) |
|---|---|
| Ports & encryption |
587 — STARTTLS <em>(recommended)</em>2525 — STARTTLS25 — STARTTLS |
| Username | the Server API Token (or the SMTP Access Key) |
| Password | the same Server API Token (or the SMTP Secret Key) |
| Authentication | Postmark uses the server token as both username and password; per-server SMTP access/secret keys are an alternative. Message streams are chosen with the X-PM-Message-Stream header. |
How to set up Postmark SMTP
- Servers → your server → API Tokens → copy the Server API Token.
- Sender Signatures → add the domain → DKIM and Return-Path DNS records.
- App settings: host smtp.postmarkapp.com, port 587, STARTTLS, username = token, password = token; add header X-PM-Message-Stream: outbound.
Sending limits
- Free developer tier: 100 emails per month; paid from $15/month for 10,000.
- Transactional streams must not carry marketing mail; broadcast streams require unsubscribe handling.
- Sender signature or verified domain (DKIM + Return-Path) required.
Things that catch people out
- Test accounts (unapproved) can only send to addresses on the same domain as a sender signature.
Common Postmark SMTP errors
| Server reply | Meaning | Fix |
|---|---|---|
535 5.7.8 Authentication failed | Token wrong, or username/password not identical. | Use the server token for both. |
550 Sender signature not confirmed | From not verified. | Confirm the sender signature/domain. |
More codes: 535 authentication failed, 550 relay denied, 554 rejected as spam, connection timed out — or all SMTP error codes.
When Postmark is not enough for your app
When a provider caps you or blocks a port, point the same app at QueenSMTP instead: host smtp.queensmtp.com, port 587 (STARTTLS) or 465 (SSL), your SMTP username and password from the dashboard. $5/year plus $0.10 per 1,000 emails, 100 free a day to test.
Get SMTP credentials — free to test Test Postmark nowRelated settings
Postmark SMTP — questions
smtp.postmarkapp.com on port 587 (or 2525/25) with STARTTLS; use the Server API Token as both username and password.
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