function checkRequiredFields(input)
{

    var requiredFields = new Array("name",
                                   "mail",
                                   "phone",
                                   "message");

    var fieldNames = new Array("name",
                               "mail",
                               "phone",
                               "message");
    var fieldCheck   = true;
    var fieldsNeeded = "\nPlease fill out all fields!\nThese are still empty:\n\n\t";

    for(var fieldNum=0; fieldNum < requiredFields.length; fieldNum++) {
        if ((input.elements[requiredFields[fieldNum]].value == "") ||
            (input.elements[requiredFields[fieldNum]].value == " ")) {

            fieldsNeeded += fieldNames[fieldNum] + "\n\t";
            fieldCheck = false;
        }
    }

    if (fieldCheck == true)
    {
        return true;
    }
    else
    {
        alert(fieldsNeeded);
        return false;
    }
}