Sending, receiving, and organizing email in Outlook.com
Hi,
I will walk through a few steps with you. Some of these are just to help figure out what is wrong, not to fix it right away. So if nothing changes after a step, that is normal. I will keep going until we solve it.
If you go to https://onedrive.live.com/largestfiles page to verify the largest files and https://onedrive.live.com/?view=1&v=managestorage&sw=bypassConfig to view the Storage space, does it help you out in anyway?
For your information that for me, these pages are not working due to an ongoing Microsoft outage, so it may not work for you, and it also might be the case that you are having these issues due to the same outage as well.
Before trying anything else, I recommend waiting a few hours until the outage is resolved.
I look forward to hearing from you to get the results of the troubleshooting.