Microsoft’s Hotmail and Outlook servers are having issues today. According to their status page:

Hotmail
We're having a problem accessing email. You might not be able to see all your email messages. We're working to restore service right now.

Problem: We're having a problem accessing email. You might not be able to see all your email messages. We're working to restore service right now. Mar 12 5:35 PM
Updates: Fixing the problem is taking longer than we hoped. We'll provide an update by Mar 13 9:12 AM. We apologize for the lengthy interruption in service. Mar 13 5:11 AM

Outlook
We're having a problem accessing email. You might not be able to see all your email messages. We're working to restore service right now.

Problem: We're having a problem accessing email. You might not be able to see all your email messages. We're working to restore service right now. Mar 12 5:35 PM
Updates: Fixing the problem is taking longer than we hoped. We'll provide an update by Mar 13 9:12 AM. We apologize for the lengthy interruption in service. Mar 13 5:11 AM

Keep an eye on the issues at https://status.live.com