try{
String msg=\"Happy BirthDay Dear, \"+name.toUpperCase()+\" !!! Have a Great Day. \\n \\n Thank You \\n Seva Development \";
You didn't specified content type of mail. In which case it is sent in plain.
Try setting content type
helper.setContent(htmlMsg, "text/html; charset=\"utf-8\"");
Now when you open this mail with any email client, it will read it in html format.
You can also set multiple formats by using MimeMultitype
Multipart multipart = new MimeMultipart("alternative");
BodyPart messageBodyPart;
// PLAIN TEXT
messageBodyPart = new MimeBodyPart();
messageBodyPart.setContent(textBody, "text/plain; charset=\"utf-8\"");
multipart.addBodyPart(messageBodyPart);
// HTML TEXT
messageBodyPart = new MimeBodyPart();
messageBodyPart.setContent(htmlBody, "text/html; charset=\"utf-8\"");
multipart.addBodyPart(messageBodyPart);
message.setContent(multipart);