使用mail（）的jQuery AJAX表单PHP脚本发送电子邮件，但HTML表单中的POST数据未定义

Thanks for taking the time to look, guys. I'm creating a pretty basic AJAX contact form using jQuery. The email sends, but upon opening the email there is no POST data, so I just get the strings I defined in the PHP script. On my phone's email client, the content of the email literally says 'undefined'. I've tried adding different types of header data to no avail, and a number of variations on the PHP mail() function. Thanks for taking the time to look, guys. I'm c