Using text for variable in function

Question

I've got the following code. I have tried a lot but I can't find the solution to use the text of the "messages" for the "errorMessage : message". What am I doing wrong?

$.formUtils.addValidator({
    name: "checkemail",
    validatorFunction: function(value, $el, config, language, $form) {
        var message = "Error";
        $.post("system/ajx/check_email.php", {
            "email": value
        }, function(data) {
            if (data == "ER1") {
                message = "Email fehlerhaft";
                result = false;
            } else if (data == "ER2") {
                message = "Trashmaildienste nicht erlaubt";
                result = false;
            } else if (data == "ER3") {
                message = "Email schon registriert bitte einloggen!";
                result = false;
            } else if (data == "true") {
                message = "";
                result = true;
            } else {
                message = "sonstiger Fehler";
                result = false;
            }
            alert("Result: " + data);
        });

        //return true oder false
        return result;
    },
    errorMessage: message,
    errorMessageKey: "badEvenNumber"
});