Dart

Add a Custom Header to an Email Attachment

Demonstrates the Chilkat Email.AddAttachmentHeader method, which adds a custom MIME header field to an existing attachment identified by its zero-based index. This example adds an attachment (which becomes index 0), then attaches an extra header field to it and prints the resulting MIME.

Background: In MIME, every attachment is itself a mini-message with its own small block of headers — things like Content-Type, Content-Disposition, and Content-Transfer-Encoding that describe that specific part. AddAttachmentHeader lets you insert additional fields into that per-part header block, which is occasionally needed for interoperability with systems that look for custom X- headers or content identifiers on individual attachments.

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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // Demonstrates the AddAttachmentHeader method, which adds a custom MIME header field to
  // an existing attachment, identified by its zero-based index.

  final email = CkEmail();
  email.subject = 'Attachment with a custom header';
  email.body = 'The attachment has an extra MIME header.';

  // Add an attachment; it becomes attachment index 0.
  email.addStringAttachment('data.txt', 'Attachment body.');

  // Add a custom header field to the first attachment (index 0).
  email.addAttachmentHeader(0, 'X-Custom-Attachment-Header', 'some value');

  // The custom header now appears in the attachment's MIME part.
  print(email.getMime());
}