--- lists.module.orig	2008-07-10 11:51:35.000000000 -0400
+++ lists.module	2008-07-10 11:59:44.000000000 -0400
@@ -125,6 +125,7 @@
     '#default_value' => ($user->uid ? $user->mail : ''),
     '#size'          => 50,
     '#maxlength'     => 255,
+		'#required' 		 => true,
   );
   $form['item'] = array(
     '#type' => 'item',
@@ -147,6 +148,13 @@
   return $form;
 }
 
+function lists_subscribe_validate($form_id,$form) {
+	if(!valid_email_address($form['mail']))
+	{
+		form_set_error('mail',t("Please enter a valid email address."));
+	}
+}
+
 function lists_subscribe_submit($form_id, $form = NULL) {
   $flag = FALSE;
   $mail = $form['mail'];