Exchange Online determines the closest EXO front door by the location of resolver. Other M365 services do not use this method, it is an artifact from Exchange Server.
EDIT: This is outlined in [0], although it doesn't go into the depth I wish it did.
> By providing local Internet egress and by configuring internal DNS servers to provide local name resolution for Microsoft 365 endpoints, network traffic destined for Microsoft 365 can connect to Microsoft 365 front end servers as close as possible to the user.
EDIT: This is outlined in [0], although it doesn't go into the depth I wish it did.
> By providing local Internet egress and by configuring internal DNS servers to provide local name resolution for Microsoft 365 endpoints, network traffic destined for Microsoft 365 can connect to Microsoft 365 front end servers as close as possible to the user.
[0] https://learn.microsoft.com/microsoft-365/enterprise/microso...