Which OWA URL will be displayed :
User's mailbox moved to 2016
User's mailbox remains on 2010
All EXCHs are in DAG (1 DAG for mbx 2010 and 1 DAG for mbx 2016)
EXCH 2010 = CAS/HUB
EXCH 2010 = 2 MBX
EXCH 2016 = 3 CASES (all roles)
EXCH 2016 = 3 MBX
So, coexistence mode.
For me, the user will have the OWA 2016 in all cases displayed first.
Then once logged in, if his box is under 2016 he stays under OWA 2016, if his box is under 2010 then the OWA 2010 URL is displayed.
Thanks for the clarification. :)