Default encoding not able to transmit special characters

[stephtr]

The default encoding for addMessage is 7 bit / utf-8, which, as far as I know is kind of a contradiction. When sending mails including umlauts, in some email programs they are thus not displayed correctly.
The proper way would be to use:

msg.addMessage({ contentType: 'text/plain', data: quotedPrintableEncode(text), encoding: 'quoted-printable' });

But wouldn't it make sense to make this the default of MIMEText? eg.:

• If encoding/charset is specified, use the text as-is.
• If no encoding/charset is supplied, switch to quoted-printable and escape the text. As characters outside the 7-bit range are anyway illegal in the current state, this wouldn't even be a breaking change.

For reference, that's the function ChatGPT provided me and which works for me:

function quotedPrintableEncode(input: string): string {
    const encoder = new TextEncoder(); // encodes to UTF-8 bytes
    const bytes = encoder.encode(input);
    let result = '';
    let lineLength = 0;
  
    const softBreak = () => {
      result += '=\r\n';
      lineLength = 0;
    };
  
    for (let i = 0; i < bytes.length; i++) {
      const byte = bytes[i];
  
      // Printable ASCII range excluding '=' (equals)
      const isPrintable =
        (byte >= 33 && byte <= 60) || (byte >= 62 && byte <= 126);
  
      let toAppend;
  
      if (byte === 0x3D || !isPrintable) {
        // Needs encoding (e.g. "=" or non-printable)
        toAppend = '=' + byte.toString(16).toUpperCase().padStart(2, '0');
      } else {
        toAppend = String.fromCharCode(byte);
      }
  
      // Line length: soft wrap at 76 characters
      if (lineLength + toAppend.length > 75) {
        softBreak();
      }
  
      result += toAppend;
      lineLength += toAppend.length;
    }
  
    return result;
}

Great work btw!!