What is Trash/Archive Folder? What is the Difference Between Delete and Archive? What is Archive?
Archive usually keeps the mail in Archive Folder, for future reference. Delete commonly puts the mail in a Trash folder, that is periodically cleaned, and can also be manually deleted forever on demand. You can access both of those folders from the Folders pane.
You can View your Folders using: Swipe from left edge or by tapping the top left corner logo, and choosing the desired Account. Choose Trash/Archive.