How can we get last active use of mail id's in bulk?
Using DBViewer API (https://resources.count.ly/v1.0/reference#odbdbsdbcollectioncollection)
to query App users collection (https://resources.count.ly/docs/countlyapp_usersappid)
You would sort by lac property (last access) in projection specify only email property to be returned and limit amount of users to what you want to get.
Then you can use skip parameter to get another batch of users, etc. Like pagination