To start the PopProxy was challanging, generally you change ServerComponentState using the maintenance requester for most components. However running the following command did nothing:
Set-ServerComponentState -State Active -Requester Maintenance -Component PopProxy -Identity AB-EXCH-01
To start the PopProxy component, I needed to use the Exchange 2013 Health API as a requester.
Set-ServerComponentState -State Active -Requester HealthAPI -Component PopProxy -Identity AB-EXCH-01