I have a list of about 5,000 opted in leads that were provided to me. I'm not sure of the age of these leads. Basically I want to wash them and verify that they are still valid and remove the ones that are not longer interested and opted out. What would be the most effective and economical way to take my list and refine it to filter out the good leads from the leads that are no longer interested? If I just send all of the leads an email asking them, I fear they would just be annoyed and request to be taken off the list. What is the best approach here?