Currently when a user unsubscribes they are removed from all public lists.

Proposed change is to set them as disabled. This allow for mass imports from
other system that don’t override a decision to unsubscribe. (One of my clients
has a 60,000+ list)

The following code change in action.unsubscribe.php achieves the above

From:
$query = "SELECT A.listid FROM ".NMS_LIST_TABLE." A, ".
  NMS_LISTUSER_TABLE." B WHERE A.listid = B.listid AND A.public = 1 
  AND B.userid = ?";
  
$q2 = "DELETE FROM ".NMS_LISTUSER_TABLE." WHERE userid = ? AND listid = ?";

$dbresult = $db->Execute($query,array($userinfo['userid']));

if( !$dbresult )
  {
    echo $db->ErrorMsg();
    return;
  }
while( $row = $dbresult->FetchRow() )
  {
$dbresult2 = $db->Execute( $q2, array( $userinfo['userid'], $row['listid']
));
  }

To: 

$query = "UPDATE cms_module_nms_users SET disabled = 1 WHERE userid = ?";

$dbresult = $db->Execute($query,array($userinfo['userid']));

if( !$dbresult )
  {
    echo $db->ErrorMsg();
    return;
  }