try{ String msg=\"Happy BirthDay Dear, \"+name.toUpperCase()+\" !!! Have a Great Day. \\n \\n Thank You \\n Seva Development \";
Since you are using MimeMessageHelper .Try below.
MimeMessageHelper
MimeMessageHelper helper = new MimeMessageHelper(message,true); helper.setText(msg, true);
Use MimeMessageHelper.setText(emailContent,true) method. The boolean true flag indicates html content.
true