Annoying message- Outlook

Hi I was wondering if anyone could assist me in getting rid of this annoying pop up from (purportedly) Outlook? You can see in the attached .jpg the pop up, and every time you click "OK" it simply pops up again. The password is correct and I know this because I am still able to send and receive any mail, it is just annoying! I tried installing icloud for Windows (didnt do anything), and clicking "Repair" against the entry in the Outlook settings, but no luck so far. (It was unable to repair it and said it could not connect to icloud server. Yet it still works.) I also checked the manual settings in Outlook from the Apple icloud server in the help page here
... but they are correct.

I cannot see any attachment. I think you can turn them off in settings/notifications.

Hi Gary, thanks for your message, I had some problems uploading the screenshot, I think it is visible now? this is what I meant when I mentioned the "attachement".