you can alternatively write code like this ,
Multipart _multipart = new MimeMultipart("test");
for (String str : attachment_List) {
MimeBodyPart messageBodyPart = new MimeBodyPart();
DataSource source = new FileDataSource(str);
messageBodyPart.setDataHandler(new DataHandler(source));
messageBodyPart.setFileName(source.getName());
multipart.addBodyPart(messageBodyPart);
}
_msg.setContent(_multipart);
Transport.send(_msg);
solved Working code that sends only one attachment