Since you add a exchange tag to your question,I suppose that you have a exchange on-premise server.
Do other users have the same problem? Or it just occurs on your account.
And are you using Outlook for PC? If you delete a mail via OWA, will it still return in inbox?
If OWA is working fine and the problem is just with Outlook for PC, please remove and recreate your outlook profile and see if the problem persists.
Remove a profile
Create an Outlook profile
If it doesn't help with your problem,please provide some more information so that we can give more appropriate suggestions.
For example,are you using other clients like mail apps for ios or android at the same time?
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