Non-restrictive email validation
Your code would be slightly nicer this way:

jQuery.validator.addMethod("easyEmail", function(value, element, param) {
    if (this.optional(element)) {
        return true;
    }
    var trimmed = $.trim(value);
    var index = trimmed.indexOf('@');
    return index &gt; 0 &amp;&amp; index &lt; trimmed.length - 1;
}, "Please enter a valid email address.");


Slightly nicer, because:


Check element before trimming value, as you might not use value at all.
It's a good practice to not overwrite parameter variables
It's good to cache the result of .indexOf to avoid calling twice


That said, since @user45891 found that nice link for you, I recommend you use it. I understand you only want a super-simple email validation, but this is waaaay too simple, to the point of almost uselessness.