If you are familiar with Gmail, you're probably already familiar with archiving mail opposed to fully deleting it. You also have this option for iCloud mail as well. If you prefer archiving certain items for access later while deleting things you won't ever need again, follow along and we'll show you how.
That's all there is to it. Your messages can now be stored in an archive folder if you choose instead of being moved automatically to trash. You'll now see an option to archive or trash when cleaning up messages.