When you delete a message from your Inbox, it is sent to a Trash folder for that account. If you would like to permanently delete the messages in this folder, take the following steps:
- Tap on the menu (hamburger icon) on the top left and scroll down to Accounts
- Tap on the account you would like to permanently delete messages from. You will see the list of folders for that account
- Scroll down and tap on the Trash folder.
- Within this folder you can swipe left to permanently delete a message, or tap and hold to select multiple messages at once.