Ejemplo

public static void main(String[] args) {
javax.mail.internet.MimeMessage mm = new javax.mail.internet.MimeMessage(
javax.mail.Session.getInstance(new java.util.Properties()));
try {
mm.setText(args[0]);
byte[] description = ((String) mm.getContent()).getBytes();
java.io.FileOutputStream out = new java.io.FileOutputStream(
"Rule.html", true); //$NON-NLS-1$
out.write(description);
} catch (Exception e) {
System.out.println(e.toString());
}
}

Solución

Utilice
javax.mail.internet.MimeBodyPart.setText (java.lang.String, java.lang.String) La serie de Unicode se codificará mediante el conjunto de caracteres especificado.
Fíjese en que el conjunto de caracteres especificado debe soportar todos los caracteres de la serie.
Si el lenguaje de la serie es desconocido, utilice UTF-8.

public static void main(String[] args) {
String text = args[0];
String charset = args[1];
javax.mail.internet.MimeMessage mm = new javax.mail.internet.MimeMessage(javax.mail.Session.getInstance(new java.util.Properties()));
try {
mm.setText(text,charset);
byte[] description = ((String)mm.getContent()).getBytes("UTF-8"); //$NON-NLS-1$
java.io.FileOutputStream out = new java.io.FileOutputStream("Rule186-2.html", true); //$NON-NLS-1$
out.write(description);
}catch (Exception e){
System.out.println(e.toString());
}
}