Editing

So, how do you decide when to stop sending someone Christmas cards? I always struggle with this, particularly if I haven't heard anything from their end for a while. There's no way to tell if they're happy to get your card or if it goes straight into the recycling unopened. Any of you have a good rule of thumb on this one? If someone moves and you don't have their new address, how much of an effort do you make to track them down to keep sending them missives that may, after all, be unwanted?