Oddly enough, organization-wide settings are given a second billing, underneath the section for managing users, but this is probably the first place you'll want to go when you first set up your tenant. 

Settings are organized into two tabs: general and external communications:

Skype general organization-wide settings

In the general tab, there are only three settings: presence privacy mode, Microsoft Push Notification Service, and Apple Push Notification Service.

Let's consider presence privacy mode for a moment. By default, anyone can access your presence information—whether they're in your Skype for Business contacts list or not. While we cannot confirm this, we interpret this to mean that those who are able to may be able to invade your privacy by coding against Skype's APIs and guessing your SIP address from your email address. Therefore, we recommend that you should set this to Display presence information only to a user's contacts.

According to Microsoft...