Test for a valid e-mail address and MX records in PHP

Tests for a valid email address and optionally tests for valid MX records, too.

    function is_valid_email($email, $test_mx = false) {
        if (eregi("^([_a-z0-9-]+)(\.[_a-z0-9-]+)*@([a-z0-9-]+)(\.[a-z0-9-]+)*(\.[a-z]{2,4})$", $email)){
            if ($test_mx) {

                list($username, $domain) = split("@", $email);

                return getmxrr($domain, $mxrecords);
            } else {
                return true;
            }

        } else {
            return false;
        }
    }

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