How to get rid of pop up in Outlook?

[Hof525@hotmail.com]

Ok, so I keep getting this pop up notice in Outlook that says that "you must enter your username and password for the following server". It pop ups every few seconds. I keep putting in this information and it keeps happening. I thought that maybe I was using another password so I tried everything i could think of. Then I thought if changed my password that would solve the problem. I went to the Microsoft sign page, put in my email and and it says it doesn't exist! The weird thing is that I can use my email if I click on something quickly, and I mean very quickly, in between the pop ups. So obviously it does exist! I even had to use my personal email to log into this site to ask a question! I am using Windows 8 and think my Outlook is 2016.

Can anyone help?
Thanks!