Why has comcast taken away the bulk delete option where you could delete all then go through the list and individually select the ones you want to keep. The new option to only delete all emails in this folder or to have to go through each and every email you want to delete and click on them individually is a stupid option
Do you mean you want to "Select all"? If so, all you have to do is check any message in the list, then on your keyboard hit Cntrl-A. That will select everything in the list on that page. Then you can de-select any you want to keep. Then just hit the Trashcan icon in the toolbar.