My customer requires that a particular LAN host should only be able to access outlook.office365 and skype for business and messenger, blocking all other websites.
Any idea how to configure the policy for allowing skype.
This seems to contain the list of servers and ports we need to work on. You may create a policy with the required information and apply the same on the desired device.
Hope this helps you. [I am sure you know how to create and apply a policy]
You need to allow traffic between your subnet and the Microsoft cloud and the link provided by @AjitKumar has all the details you may need to configure rules on the MX.