These instructions require you to have outlook installed on a windows desktop/laptop.
1. Go to Outlook and right click on inbox to where you see your folders (if you don’t see click the > arrow on the left near the top).
2. Select the folder you want to archive - commonly Inbox or Sent Items (if you have multiple sent folder you can do this on more than one).
3. Then right click on 'Properties'.
4. Click 'AutoArchive' tab on top.
5. Select 'Archive this folder using these settings' and you can adjust as needed but maybe 6 months is good.
6. Then Click 'Apply'.