I don't think you can turn JavaScript objects into JSON strings using only jQuery, assuming you need the JSON string as output.
Depending on the browsers you are targeting, you can use the JSON.stringify function to produce JSON strings.
See http://www.json.org/js.html for more information, there you can also find a JSON parser for older browsers that don't support the JSON object natively.
In your case:
var array = [];
$("input[class=email]").each(function() {
array.push({
title: $(this).attr("title"),
email: $(this).val()
});
});
// then to get the JSON string
var jsonString = JSON.stringify(array);