When using an account with Multi-factor Authentication enabled, certain applications (like Skype for Business) require specialized logins.
Be sure to generate a new password for each App (Skype for Business). Since passwords
can't be retrieved after they've been generated, be sure to store them in a safe place.
To generate an App Password:
First, log in to: https://mysignins.microsoft.com/security-info
Choose "Security Info" and click "+ Add method"
On the "Add a method" page, select "App password".
Give a name to the password that's generated. Creating a different password for each app is best practice.
A semi-permanent password will be created. Be sure to keep this password safe since it bypasses the multi-factor authentication system. Also, once this page is closed, it's not possible to retrieve the same password. It will be necessary to generate a new app password if this one is lost.