Im in the process of putting together a project plan for a migration of a 50 person office to exchange online .
The big risk I have identified is that we begin to change the workflow over and for some unforeseen reason mail is not routed to either the exchange online or the existing server .
Is there a point in the process that the mail is routed to both locations so we dont face that risk ?
I am assuming that everything goes fine but it is my responsibility to assume the worse and plan for it .
What are the areas that could affect the mail flow and how would i mitigate during the 72 hour time period we are taking this move ?