Q. Can Azure and Office 365 share an ExpressRoute circuit?
A. Technically an ExpressRoute circuit has a single service key that supports three peerings which is private (Azure virtual network), public (Azure services) and Microsoft (Office 365, CRM etc). This means it is possible to share a single ExpressRoute circuit across Azure and Office 365 services. There is a but. Different ExpressRoute partners architect their solutions in different ways. This means just because technically ExpressRoute CAN handle all three peer workloads on a single circuit the actual partner may implement differently and some implement one peer per service key but may allow multiple service keys on one circuit. You would need to talk to your ExpressRoute partner and discuss how they implement to understand if Azure and Office 365 could share a single circuit but technically they can.