As a cloud service, Microsoft 365 components are not available on the internal network. Network administrators must allow internal users to access the internet endpoints for the Microsoft 365 service, which may mean configuring existing appliances such as firewalls and proxy devices.

Endpoints, which can be IP addresses or URLs, are classified into three categories:

• Optimize: Required for connectivity to Office 365 services and represent over 75% of the consumed bandwidth
•  Allow: Required for connectivity, but not as sensitive to latency as optimize endpoints
• Default: Endpoints that can be treated as normal internet traffic

Organizations should plan for network best practices when planning their Office 365 deployment. Among the recommended practices are the following:

• Differentiating Office 365 traffic from normal internet traffic.
• Egress network connections locally so that users will be routed as quickly as possible to the Microsoft network.
• Bypassing proxies to reduce the amount of time needed for data to arrive at Office 365 services.

Microsoft 365 administrators and network administrators should work together to plan a network connectivity strategy. To help plan effectively, Microsoft provides a web service for obtaining the IP addresses and URLs that are used in the service.  

Microsoft typically recommends bypassing proxy devices for network traffic destined for Microsoft 365.