diff -Nur osticket_1.6.rc2/upload/include/class.validator.php osticket_1.6.rc2-patch5/upload/include/class.validator.php
--- osticket_1.6.rc2/upload/include/class.validator.php	2008-01-01 04:40:46.000000000 +0100
+++ osticket_1.6.rc2-patch5/upload/include/class.validator.php	2008-01-24 13:03:00.000000000 +0100
@@ -125,9 +125,37 @@
     }
    
     /* Functione below can be called directly without class instance. Validator::func(var..); */
+    /* RFC 2822 syntaxic check */
+    /* derived from http://www.ilovejackdaniels.com/php/email-address-validation/ */
     function is_email($email) {
-        return eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,4})$",trim($email));
+        // First, we check that there's one @ symbol, and that the lengths are right
+        if (!ereg("^[^@]{1,64}@[^@]{1,255}$", $email)) {
+          // Email invalid because wrong number of characters in one section, or wrong number of @ symbols.
+          return false;
+        }
+        // Split it into sections to make life easier
+        $email_array = explode("@", $email);
+        $local_array = explode(".", $email_array[0]);
+        for ($i = 0; $i < sizeof($local_array); $i++) {
+           if (!ereg("^(([A-Za-z0-9!#$%&'*+/=?^_`{|}~-][A-Za-z0-9!#$%&'*+/=?^_`{|}~\.-]{0,63})|(\"[^(\\|\")]{0,62}\"))$", $local_array[$i])) {
+             return false;
+           }
+        }  
+        if (!ereg("^\[?[0-9\.]+\]?$", $email_array[1])) { // Check if domain is IP. If not, it should be valid domain name
+          $domain_array = explode(".", $email_array[1]);
+          if (sizeof($domain_array) < 2) {
+              return false; // Not enough parts to domain
+          }
+          for ($i = 0; $i < sizeof($domain_array); $i++) {
+            if (!ereg("^(([A-Za-z0-9][A-Za-z0-9-]{0,61}[A-Za-z0-9])|([A-Za-z0-9]+))$", $domain_array[$i])) {
+              return false;
+            }
+          }
+        }
+
+        return true;
     }
+
     function is_phone($phone) {
         $stripped=eregi_replace("(\(|\)|\-|\+)","",ereg_replace("([  ]+)","",$phone));
         return (!is_numeric($stripped) || ((strlen($stripped)<7) || (strlen($stripped)>13)))?false:true;