Okay, so you deleted an email in your university https://outlook.office365.com/mail/
But you go to the Deleted Items folder, and the emails are still there, available for Recovery.
Go to the Deleted Items folder.
Click the Recover link
Look at all the emails that have popped up in a list. For each one that you want to PERMANENTLY DELETE, right-click on the Garbage can to the right of the email listing.
Click DELETE.
“Do you want to PERMANENTLY DELETE the email?”
OK
Now, Outlook is squirrelly. You should go back to the Deleted Items folder.
Where you see “Recover items deleted from this folder (x items)”, click on the Garbage can on the upper left. Click it, or, get the radio button to check that will allow you to Select All emails.
A window should open up that allows you to Empty Folder. Click it.
If you still see that there are items left to Recover, click that link and go through the same process. You will get a window to the right that gives you an “Empty Folder” option.
When you see ZERO ITEMS left to Recover, you are done.