When you delete a message, the following events occur:
The message is moved to your Trash folder.
If your Inbox is configured to show deleted messages, the message appears in your message list, in strikethrough format. To show deleted messages, choose View -> Hide Deleted Messages so that the Hide Deleted Messages menu item is deselected.
If you need to retrieve a message from Trash, you can undelete the message. When you undelete a message, the message is restored to the folder from which you deleted the message.
You can expunge a folder to remove permanently from the folder the messages that you deleted.
You can empty your Trash folder to delete the contents of Trash permanently. That is, when you empty Trash, you expunge all your folders.
Select the message that you want to delete in the message list, then choose Edit -> Delete.
Select the message that you want to undelete in the Trash folder, then choose Edit -> Undelete.
To delete permanently the messages from a folder, open the folder, then choose Actions -> Expunge.
Choose Actions -> Empty Trash.