A con of building an own solution is that it probably takes more time than installing a plugin for example, Wordpress. However, the plugins comes with the con that you don’t know exactly whats in them without really looking through the code. If the plugin is very popular there may also...
jQuery will handle the AJAX using$.postmethod and jQuery Validation plugin will validate the field values including email address format. <html> <head> <title>MailChimp Sign-Up Form</title> <scripttype="text/javascript"src="js/jquery-1.11.0.min.js"></script> ...