Hotmail, Outlook, etc... is forcing a verification code.
If you start having problems with X-Notifier not checking Hotmail/Outlook/Live.com... then manually open a new tab in your browser and manually go to hotmail.com or outlook.com or live.com... and sign in. You may get a prompt from Microsoft that they need you to enter a code that they will email you.
Microsoft is forcing this 'verification' code on some users, and it interferes, like any miscellaneous automatic prompt can, with X-Notifier.