In the Trash folder you don't. When you delete an email it goes to Trash and will remain there for 14 days. After that it will drop into the Recovery folder. It will stay in there for 30 days and will then permanently drop out and can no longer be recovered. So 14 days in the Trash folder is the default, and there is no way for you to change that. So if you think you might want to find something older you could create a folder of your own and start moving messages there instead of using the Trash folder. To view the recovery folder, right-click on the Trash folder, then click on "Recover deleted items".