Erase Deleted Emails in Outlook
When you delete emails in Inbox folder, they don't really disappear but go into the deleted items folder, so you need one more step to "permanently" delete them: Empty the deleted folder. Why I put a quotation mark on the word "permanently"? Because that's not really permanently delete operations, just like the prompt shows when you press Shift+ Delete together to delete a file. The prompt is to tell you the file you deleted will not go to recycle bin, so it can be recovered by third party software.
Let's go through the steps to permanently delete emails in outlook:
1. Click Delete Items option in the navigation pane and press Ctrl+A to choose them all.
2. Click Delete or Ctrl+D to delete deleted items. If you don't want to do this manually every time you exit, you can set this operation to run automatically when closing outlook.
3. Click File tab > Options > Advanced, check the Empty the Deleted Items folder upon exiting box under Outlook Start and Exit. Then scroll down, check the Prompt for confirmation before permanently deleting items box. Close Outlook (2007).
4. Run ByebyeData Eraser and click Erase free space, select C Drive and choose an erase standard from the list in the right-side column. (Outlook default path locates in C Drive, if you installed it on other Drive, you can click the Drive to erase free space).
5. Click Erase Now and Confirm.
Note: These guide steps also apply to Outlook 2010, 2013, 2016.
Once you erased free space in C Drive, not only outlook deleted files cannot be recovered, but other deleted files' traces cannot be restored either. So if you want to get back the Mistakenly deleted emails, move them to inbox before you delete the emails in the deleted items folder
Tips: When you find there're emails mistakenly deleted after you pressed down Ctrl+A, you can hold the Ctrl button and click these emails one by one to exclude them. After you press deleted button or Ctrl+D, the excluded emails left behind, you can then move them to Inbox folder again.