How do I clean up emails in Outlook?
If you use e-mail via IMAP, deleted mails are not immediately removed from the server but are marked for deletion. So they are still on the server and taking up space there. Sometimes you just want to clear all emails from a folder, the option described below can be helpful for this.
When you want to delete mails permanently, there is an option to empty that folder:
Then just confirm and the emails are gone for good.