When you delete an email, you will then find the email in the Deleted Items folder.
This help article explains how to empty the trash and permanently delete emails.
Emptying the trash
- Open the trash by clicking the Deleted Items folder
- Click the cog (at the bottom left)
- Click Empty
- Confirm that you would permanently like to delete the emails by clicking OK
Tip: You can also empty the trash by right-clicking the trash folder and then clicking Empty.