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Postmark Invalid Custom Header

A custom header in the email request is not formatted correctly.

Understanding Postmark: A Reliable Email Communication API

Postmark is a robust email communication API designed to deliver transactional emails swiftly and reliably. It is widely used by developers to ensure that their applications can send emails with high deliverability rates. Postmark provides a range of features including email templates, analytics, and custom headers to enhance email functionality.

Identifying the Symptom: Invalid Custom Header

When using Postmark, you might encounter an error related to an 'Invalid Custom Header'. This issue typically manifests when an email request is made with improperly formatted custom headers, leading to failed email delivery or unexpected behavior.

Exploring the Issue: What Causes Invalid Custom Headers?

Custom headers in emails allow developers to include additional metadata that can be used for tracking, categorization, or other purposes. However, if these headers are not formatted correctly, Postmark will reject the request. Common formatting errors include missing colons, incorrect casing, or unsupported characters.

Common Mistakes in Custom Header Formatting

  • Missing colon between the header name and value.
  • Using unsupported characters in header names.
  • Incorrect casing of header names.

Steps to Fix the Invalid Custom Header Issue

To resolve the 'Invalid Custom Header' issue, follow these detailed steps:

Step 1: Review Your Custom Headers

Carefully inspect the custom headers in your email request. Ensure that each header follows the correct format: Header-Name: HeaderValue. Check for any missing colons or unsupported characters.

Step 2: Validate Header Names

Ensure that your header names are correctly cased and do not contain any special characters. Refer to the Postmark Custom Headers Guide for a list of supported header formats.

Step 3: Test Your Email Request

After making the necessary corrections, test your email request to verify that the headers are now valid. You can use tools like Postman to simulate the request and check for errors.

Conclusion

By ensuring that your custom headers are correctly formatted, you can prevent the 'Invalid Custom Header' error and maintain the reliability of your email communications through Postmark. For more detailed information, visit the Postmark Support Page.

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