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Emails do not include custom headers when using the Microsoft Graph API

Updated on April 6, 2022

Some implementations of custom headers cause delivery issues, for example, empty carbon copy (CC) fields in an outbound email.

The header is a code snippet in the HTML email body that precedes the email body. Headers usually contain information about the sender, recipient, and various authentication details.


Email messages that your application distributes are missing headers.


This issue might be caused by the following implementation flaws:

  • Overridden Service Email rule definition, to enable selecting an unsupported message header type.
  • Exceeded the limit for the maximum number of custom headers in a message.
  • Formatted the header name improperly.


  • Customize headers by using an activity to send emails. Ensure that your configuration meets the following requirements:
    • The message does not include more than five custom headers.
    • The header name has the following format: "x-<header_ID>"
      Note: The x character is case-insensitive.
      For more information, see the REST Microsoft Graph API documentation.
    The following figure shows a correctly formatted custom message header in an activity:
    Adding a custom header through an activity
    A snippet from an activity in Pega that shows how to properly set a custom header for Microsoft Graph.
  • If you use a Service Email rule, for each response header, ensure that the Field Name parameter value is either Subject or From.
    Note: Do not customize the Service Email rule definition to include additional header types from the Field Name list.
    The following figure shows a sample response header in a Service Email rule:
    Service Email – Response header
    The Response tab in the Service Email rule that shows a response header.

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