Dart

Convert 8-bit MIME Parts to Base64

Demonstrates the Chilkat Mime.Convert8Bit method, which recursively converts every part whose Content-Transfer-Encoding is 8bit or binary to base64. It takes no arguments and is a void method.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: The original SMTP standard only guaranteed 7-bit transport, and some legacy servers still reject or mangle raw 8-bit and binary content. Converting those parts to base64 — a 7-bit-safe encoding — makes the whole message safe to relay through such systems without loss. It walks the entire tree, so a multipart message with several offending parts is fixed in one call.

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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  final mime = CkMime();
  try {
    mime.loadMimeFile('qa_data/message.eml');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Recursively convert every part whose Content-Transfer-Encoding is 8bit or binary to base64.
  // This makes the MIME safe to transmit over channels that only support 7-bit text (such as some
  // legacy SMTP servers).
  mime.convert8Bit();

  print('8bit/binary parts converted to base64.');
  final String mimeText;
  try {
    mimeText = mime.getMime();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print(mimeText);
}