servers directly.
Explanation:
Being a cloud service, Office 365 would be classed as an external host to the office computers.
All the offices connect to the Internet and resolve external host names by using the main office connections. This means that all branch office computers perform DNS lookups and connect to the Internet over the WAN link.
Each branch office will have a direct connection to the Internet so the quickest possible access to Microsoft 365 services would be by using the direct Internet connections. However, the DNS lookups would still go over the WAN links to main office. The solution to provide the quickest possible access to Microsoft 365 services is to configure DNS name resolution so that the computers use public DNS servers for external hosts. That way DNS lookups for Office 365 and the connections to Office 365 will use the direct Internet connections.