function searchemail()
{
var email =$('#email').val();
    alert(email);
        $.ajax({
        method: "POST",
        contentType: "application/json; charset=utf-8",
        url: "emailcheck.php",
        data: "email="+"test",
        success: function(ret){
     alert(ret);
        },
        error: function(x,e){
            alert("error occur");
        }
    })

}

<?php

echo "test"+$_REQUEST['email'];