Yes they can, in landscape, go into your trash and select the email, you will notice a file icon with an arrow on it, top right, press this and the email will shrink and your folders (inbox, draft, sent, trash) will appear on the left hand side, select Inbox and the email will then be placed here.
This is all dependent on how you have your mail set up, trash can be deleted automatically. Go to Settings - Mail, Contacts, Calendar - your mail account. A small page will load with your mail account, go down to Advanced and press this and at the top you will see Deleted Messages, select Remove and you will be given more options.
Also when you go to the Mail, Contacts, Calendar Settings you will see under the Mail section, Show, you can select which option you would like here.
Hope this helps.
iPad 2 3G 64gb