Postmark

Common errors

• AttributeError: module 'postmarker' has no attribute 'PostmarkClient'

  cause The `PostmarkClient` class is located within the `postmarker.core` submodule, not directly under the top-level `postmarker` package.
  fix Use `from postmarker.core import PostmarkClient` to correctly import the client class.

• ImproperlyConfigured: You should specify TOKEN to use Postmark email backend

  cause When using `postmarker.django.EmailBackend`, the `TOKEN` key is missing from the `POSTMARK` dictionary in your Django project's `settings.py`.
  fix Add the `POSTMARK` setting with your server API token to your `settings.py` file: `POSTMARK = {'TOKEN': 'YOUR_POSTMARK_SERVER_TOKEN'}`.

• PostmarkerException: Sender Signature not defined for From address.

  cause The 'From' email address specified in your email message has not been added and verified as a Sender Signature or a verified domain in your Postmark account.
  fix Log into your Postmark account, navigate to 'Sender Signatures', and add and verify the email address you intend to use in the 'From' field.

• PostmarkerException: Connection Timed Out

  cause This error typically occurs when your application cannot establish a connection to Postmark's SMTP servers, often due to outbound traffic on port 25 being blocked by your ISP or hosting provider.
  fix Switch your SMTP port to 2525 or 587 in your application's configuration, as Postmark supports these alternative ports to bypass common blocks on port 25.

• PostmarkerException: Authentication Failed

  cause The Postmark API token provided in your `PostmarkClient` initialization or Django settings is incorrect, contains typos, or is an Account API Token instead of a Server API Token.
  fix Verify that you are using the correct Server API Token for the specific Postmark server and ensure there are no leading or trailing spaces or other typos.

Warnings

• gotcha postmarker is a community library, not an official Postmark SDK. Postmark has no official Python SDK. postmarker is the recommended community option per Postmark's developer docs, but it is not maintained by Postmark.
  Fix: For actively maintained alternatives, use django-anymail[postmark] for Django projects, or make direct HTTP calls using requests to the Postmark REST API.
• gotcha postmarker v1.0 has no releases to PyPI in 12+ months as of mid-2025. The project may be effectively abandoned. Python 3.11+ compatibility has not been verified in recent releases.
  Fix: Test compatibility with your Python version before relying on postmarker in production. Consider django-anymail as a more actively maintained alternative.
• gotcha Field names in postmarker follow Postmark's PascalCase API convention, not Python snake_case. Code passing lowercase fields (from_email, html_body) is silently ignored or raises AttributeError.
  Fix: Use From=, To=, HtmlBody=, TextBody=, Subject= (PascalCase) as per Postmark API docs.
• gotcha PostmarkClient constructor kwarg is server_token=, not token=. An earlier version used token= — code from older tutorials passes token= and raises TypeError.
  Fix: PostmarkClient(server_token='YOUR_TOKEN')
• gotcha Use 'POSTMARK_API_TEST' as the server_token to send emails to Postmark's blackhole test environment (test@blackhole.postmarkapp.com). These emails are never delivered. Switch to a real server token for production.
  Fix: PostmarkClient(server_token='POSTMARK_API_TEST') for testing, PostmarkClient(server_token=os.environ['POSTMARK_SERVER_TOKEN']) for production.

Install

• pip install postmarker Python (community library, not official)
• pip install django-anymail[postmark] Django (recommended alternative — Anymail is actively maintained)

Imports

• PostmarkClient
  wrong:

  from postmarker.core import PostmarkClient
  postmark = PostmarkClient(token='SERVER_TOKEN')

  correct:

  from postmarker.core import PostmarkClient
  
  postmark = PostmarkClient(server_token='SERVER_TOKEN')

  The kwarg is server_token, not token. Was renamed from 'token' in an earlier version — old tutorials using token= raise TypeError.
• Django backend
  wrong:

  EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'

  correct:

  # settings.py
  EMAIL_BACKEND = 'postmarker.django.EmailBackend'
  POSTMARK = {
      'TOKEN': 'SERVER_TOKEN',
      'TEST_MODE': False,
      'VERBOSITY': 0,
  }

  postmarker ships a Django email backend. Configure via POSTMARK dict in settings, not SMTP settings.

Quickstart

Field names match Postmark API exactly (PascalCase, not snake_case). Use 'POSTMARK_API_TEST' as token to send to the test/blackhole sandbox.

import os
from postmarker.core import PostmarkClient

postmark = PostmarkClient(server_token=os.environ['POSTMARK_SERVER_TOKEN'])

# Send single email
response = postmark.emails.send(
    From='sender@example.com',
    To='recipient@example.com',
    Subject='Hello from Postmark',
    HtmlBody='<strong>Hello!</strong>'
)
print(response['MessageID'])

# Send batch
postmark.emails.send_batch(
    {
        'From': 'sender@example.com',
        'To': 'recipient1@example.com',
        'Subject': 'Batch 1',
        'TextBody': 'Hello 1'
    },
    {
        'From': 'sender@example.com',
        'To': 'recipient2@example.com',
        'Subject': 'Batch 2',
        'TextBody': 'Hello 2'
    }
)

# Test token for sandbox
# postmark = PostmarkClient(server_token='POSTMARK_API_TEST')